Bluetooth: Fix unnecessary list traversal in mgmt_pending_remove

All of the places that need to call mgmt_pending_remove already have a
pointer to the pending command, so searching for the command in the list
doesn't make sense. The added benefit is that many places that
previously had to call list_del + mgmt_pending_free can just call
mgmt_pending_remove now.

Signed-off-by: Johan Hedberg <johan.hedberg@nokia.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>