Revert "leds: triggers: Flush pending brightness before activating trigger"

This reverts commit 93ac74cd which is
commit ab477b76 upstream.

It breaks the Android kernel abi and can be brought back in the future
in an abi-safe way if it is really needed.

Bug: 161946584
Change-Id: Iac75019b57af7941f928d7c048379f5b841f8973
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>