fix: remove skip-taskbar feature on Linux.

[ckerr]

Description of Change

This doesn't work in Wayland and won't be fixed. The feature couldn't be removed in e19 due to the policy of not removing features that aren't advertised in advance in Breaking Changes, so it was listed in e19 and is being removed now for e20.

See #33226 for more information.

CC @electron/wg-releases

Checklist

• PR description included and stakeholders cc'd
• npm test passes
• PR release notes describe the change in a way relevant to app developers, and are capitalized, punctuated, and past tense.

Release Notes

Notes: Removed the skip-taskbar feature on Linux.

[deepak1556]

Should we also remove support of https://github.com/electron/electron/blob/main/docs/api/browser-window.md#winsetskiptaskbarskip for linux ? Looks like #33226 did not cover this.

[codebytere]

@ckerr we should remove this note about linux here too:

electron/docs/api/browser-window.md

Lines 180 to 182 in 21ef850

	`skipTaskbar: true`. On Linux setting `focusable: false` makes the window
	stop interacting with wm, so the window will always stay on top in all
	workspaces.

[release-clerk]

Release Notes Persisted

Removed the skip-taskbar feature on Linux.

[trop]

I have automatically backported this PR to "20-x-y", please check out #35156

[deepak1556]

@codebytere the comment #35123 (comment) still holds true, https://github.com/electron/electron/blob/main/shell/browser/native_window_views.cc#L1043-L1047 supports the feature via win.setSkipTaskbar