Revert "leds: trigger: use RCU to protect the led_cdevs list"

This reverts commit 590304b7 which is
commit 2a5a8fa8 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: Iae32769c649f3355ef21357e7c4d6867161e8662
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>