Revert portions of "ANDROID: sched: Add vendor hooks for sched."

This reverts part of commit 54f66141.

The hook android_rvh_entity_tick is not used by any vendor, so remove
it to help with merge issues with future LTS releases.

If this is needed by any real user, it can easily be reverted to add it
back and then the symbol should be added to the abi list at the same
time to prevent it from being removed again later.

Bug: 203756332
Bug: 183674818
Cc: lijianzhong <lijianzhong@xiaomi.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>
Change-Id: I92acc11802939d1ebfcc8253490193019567695d