Revert "Introduce InputConnection#reportLanguageHint()"

This reverts commit e77386e8 [1].

Reason for revert:
The protocol is not yet ready to be exposed and we are still unsure
what is the best approach.

 [1]: Ie86edafd1ed68b58f702116f561fc448fdbb57a8

Bug: 7031513
Bug: 72522601
Fix: 74087970
Test: atest CtsInputMethodTestCases
Change-Id: Ia61dc9b3d5b116199382994430fb16ee804942b3