Remove experimental image optimization feature

[atcastle]

This PR removes the experimental optimizeImages flag. This feature was designed to automatically add preload tags for images, but I was never able to get it to do a very good job of selecting the images that actually need preloading.

This feature never graduated from experimental and in fact we never even publicized it as an experimental feature for people to try.

Additionally, even if someone was using this feature, it wouldn't have a functional effect, only a performance effect (removal of some preloads).

For those reasons, I believe it is safe to remove this functionality and that it is not a breaking change.

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall decrease ✓

	vercel/next.js canary	atcastle/next.js remove-image-opt-experiment	Change
buildDuration	15s	15s	-42ms
buildDurationCached	6s	5.9s	-52ms
nodeModulesSize	359 MB	359 MB	-8.79 kB

Page Load Tests Overall increase ✓

	vercel/next.js canary	atcastle/next.js remove-image-opt-experiment	Change
/ failed reqs	0	0	✓
/ total time (seconds)	3.001	2.951	-0.05
/ avg req/sec	832.96	847.16	+14.2
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.182	1.165	-0.02
/error-in-render avg req/sec	2115.85	2145.54	+29.69

Client Bundles (main, webpack, commons)

	vercel/next.js canary	atcastle/next.js remove-image-opt-experiment	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42 kB	42 kB	✓
main-HASH.js gzip	27.9 kB	27.9 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	71.5 kB	71.5 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	atcastle/next.js remove-image-opt-experiment	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	atcastle/next.js remove-image-opt-experiment	Change
_app-HASH.js gzip	1.36 kB	1.36 kB	✓
_error-HASH.js gzip	194 B	194 B	✓
amp-HASH.js gzip	312 B	312 B	✓
css-HASH.js gzip	326 B	326 B	✓
dynamic-HASH.js gzip	2.57 kB	2.57 kB	✓
head-HASH.js gzip	350 B	350 B	✓
hooks-HASH.js gzip	919 B	919 B	✓
image-HASH.js gzip	5.01 kB	5.01 kB	✓
index-HASH.js gzip	263 B	263 B	✓
link-HASH.js gzip	2.26 kB	2.26 kB	✓
routerDirect..HASH.js gzip	321 B	321 B	✓
script-HASH.js gzip	383 B	383 B	✓
withRouter-HASH.js gzip	318 B	318 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	14.7 kB	14.7 kB	✓

Client Build Manifests

	vercel/next.js canary	atcastle/next.js remove-image-opt-experiment	Change
_buildManifest.js gzip	459 B	459 B	✓
Overall change	459 B	459 B	✓

Rendered Page Sizes

	vercel/next.js canary	atcastle/next.js remove-image-opt-experiment	Change
index.html gzip	532 B	532 B	✓
link.html gzip	545 B	545 B	✓
withRouter.html gzip	526 B	526 B	✓
Overall change	1.6 kB	1.6 kB	✓

---

Default Build with SWC (Increase detected ⚠️)

General Overall decrease ✓

	vercel/next.js canary	atcastle/next.js remove-image-opt-experiment	Change
buildDuration	18.3s	18.3s	⚠️ +49ms
buildDurationCached	6s	6.1s	⚠️ +97ms
nodeModulesSize	359 MB	359 MB	-8.79 kB

Page Load Tests Overall increase ✓

	vercel/next.js canary	atcastle/next.js remove-image-opt-experiment	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.988	2.966	-0.02
/ avg req/sec	836.76	842.96	+6.2
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.172	1.166	-0.01
/error-in-render avg req/sec	2133.87	2144.26	+10.39

Client Bundles (main, webpack, commons)

	vercel/next.js canary	atcastle/next.js remove-image-opt-experiment	Change
450.HASH.js gzip	179 B	179 B	✓
framework-HASH.js gzip	42.1 kB	42.1 kB	✓
main-HASH.js gzip	27.9 kB	27.9 kB	✓
webpack-HASH.js gzip	1.44 kB	1.44 kB	✓
Overall change	71.6 kB	71.6 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	atcastle/next.js remove-image-opt-experiment	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	atcastle/next.js remove-image-opt-experiment	Change
_app-HASH.js gzip	1.35 kB	1.35 kB	✓
_error-HASH.js gzip	180 B	180 B	✓
amp-HASH.js gzip	305 B	305 B	✓
css-HASH.js gzip	321 B	321 B	✓
dynamic-HASH.js gzip	2.56 kB	2.56 kB	✓
head-HASH.js gzip	342 B	342 B	✓
hooks-HASH.js gzip	911 B	911 B	✓
image-HASH.js gzip	5.05 kB	5.05 kB	✓
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	2.28 kB	2.28 kB	✓
routerDirect..HASH.js gzip	314 B	314 B	✓
script-HASH.js gzip	375 B	375 B	✓
withRouter-HASH.js gzip	309 B	309 B	✓
85e02e95b279..7e3.css gzip	107 B	107 B	✓
Overall change	14.7 kB	14.7 kB	✓

Client Build Manifests

	vercel/next.js canary	atcastle/next.js remove-image-opt-experiment	Change
_buildManifest.js gzip	458 B	458 B	✓
Overall change	458 B	458 B	✓

Rendered Page Sizes

	vercel/next.js canary	atcastle/next.js remove-image-opt-experiment	Change
index.html gzip	533 B	533 B	✓
link.html gzip	546 B	546 B	✓
withRouter.html gzip	527 B	527 B	✓
Overall change	1.61 kB	1.61 kB	✓

Commit: ca3a59b

[ijjk]

Thanks!