SDK / exoplayer

I didn't copy-paste the whole of
https://github.com/google/guava/wiki/UsingProGuardWithGuava because
this line seems relevant based on our current usage.

Lots of that file seems to relate to classes that are strongly
discouraged on Android:
https://github.com/google/guava/wiki/Android#specifics

I've only added this to the `common` module, since everyone that uses
ExoPlayer must depend on that. This avoids duplicating this line into
every module that has a Guava dependency.

Also remove some other warning suppressions that are defined in both
`core` and `common`.

Issue: #7904
PiperOrigin-RevId: 332203086