Revert "ANDROID: sched: Add vendor hook for update_load_sum"

This reverts commit 5cb12b53.

The hook 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: 344826816
Bug: 181105055
Cc: Chungkai Mei <chungkai@google.com>
Cc: Qais Yousef <qyousef@google.com>
Change-Id: Ibeb60f9ff17e94f2a0ebb26b16ccbeae2b4b8c03
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>