Revert "Reapply "timers: Rename del_timer_sync() to timer_delete_sync()""

This reverts commit ec8a8e23a19bbd6dbaa158c16a60560aec48b95f.

The merge conflicts are now over, so bring it back as the abi can not be
broken.

Bug: 161946584
Change-Id: I16533658044de8e0d862cc282e528ad30fd540da
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>