Fix all breaking todo comments for 3.0 (transloadit#3907)

- `@uppy/aws/s3-multipart`: remove `client` getter and setter.
  - reason: internal usage only
  - migrate: use exposed options only
- `@uppy/core`: remove `AggregateError` polyfill
  - reason: [should be polyfilled by the user](transloadit#3532 (comment))
  - migrate: install `AggregateError` polyfill or use `core-js`
- `@uppy/core`: remove `reset()` method
  - reason: it's a duplicate of `cancelAll`, but with a less intention revealing name
  - migrate: use `cancelAll`
- `@uppy/core`: remove backwards compatible exports (static properties on `Uppy`)
  - reason: transition to ESM
  - migrate: import the `Uppy` class by default and/or use named exports for everything else.
- `@uppy/react`: don't expose `validProps`
  - reason: internal only
  - migrate: do not depend on this
- `@uppy/store-redux`: remove backwards compatible exports (static properties on `ReduxStore`)
  - reason: transition to ESM
  - migrate: use named imports
- `@uppy/thumbnail-generator`: remove `rotateImage`, `protect`, and `canvasToBlob` from prototype.
  - reason: internal only
  - migrate: don't depend on this

src/server/controllers/url.js

@@ -93,7 +93,6 @@ const meta = async (req, res) => {
     return res.json(urlMeta)
   } catch (err) {
     logger.error(err, 'controller.url.meta.error', req.id)
-    // @todo send more meaningful error message and status code to client if possible
     return res.status(err.status || 500).json({ message: 'failed to fetch URL metadata' })
   }
 }
@@ -125,7 +124,6 @@ const get = async (req, res) => {
 
   function onUnhandledError (err) {
     logger.error(err, 'controller.url.error', req.id)
-    // @todo send more meaningful error message and status code to client if possible
     res.status(err.status || 500).json({ message: 'failed to fetch URL metadata' })
   }