D-Bus: Fix P2P persistent group removal from non-D-Bus triggers

D-Bus: Fix P2P persistent group removal from non-D-Bus triggers

It is possible for the persistent group object to be added and removed
by non-D-Bus triggers (e.g., ctrl_iface commands). The add part was
already handled, but removal was not. That resulted in memory leaks when
a P2P persistent group was removed without using an explicit D-Bus
command for this even if the object was added without D-Bus involvement.

Signed-off-by: Jouni Malinen <j@w1.fi>