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

This reverts commit 7118f979 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: I504fb7dbfa49fb2d1b79107fc35325b9d5bc399d
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>