Revert^2 "Promote IgnoredPureGetter and ReturnValueIgnored to errors" am: c5f6763eb1

Original change: https://android-review.googlesource.com/c/platform/external/error_prone/+/3292763

Change-Id: I1e277261c4920899c74143396520cb18b8a9b158
Signed-off-by: Automerger Merge Worker <[email protected]>