Clean up 19.1.1 changelog (#34023)

See
https://github.com/facebook/react/pull/34021#issuecomment-3128006800.

The purpose of the changelog is to communicate to React users what
changed in the release.

Therefore, it is important that the changelog is written oriented
towards React end users. Historically this means that we omit
internal-only changes, i.e. changes that have no effect on the end user
behavior. If internal changes are mentioned in the changelog (e.g. if
they affect end user behavior), they should be phrased in a way that is
understandable to the end user — in particular, they should not refer to
internal API names or concepts.

We also try to group changes according to the publicly known packages.

In this PR:

- Make #33680 an actual link (otherwise it isn't linkified in
CHANGELOG.md on GitHub).
- Remove two changelog entries listed under "React" that don't affect
anyone who upgrades the "React" package, that are phrased using
terminology and internal function names unfamiliar to React users, and
that seem to be RN-specific changes (so should probably go into the RN
changelog that goes out with the next renderer sync that includes these
changes).