Revert "Replace hidden KeyEvent.isMediaKey() usages"

This reverts commit c7c1542ea3fef663c2395404e6f111dc01e625b4.

Bug: 119789707
Reason for revert: We'd better not to copy the hidden APIs, 
but instead we need to make them public or @SystemApi.

Change-Id: I4083d533f863cdda8b6de05cdea333082b84ec97
2 files changed