Revert "Bluetooth: MGMT: Protect mgmt_pending list with its own lock"

This reverts commit bdd56875 which is
commit 6fe26f69 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: Icc2f278181cb94ad70d566cc655c8034e24c9156
Signed-off-by: Greg Kroah-Hartman <gregkh@google.com>