_mcd_dispatch_operation_run_observers: don't leak the request properties twice
_mcd_dispatch_operation_run_observers: don't leak the request properties twice

observer_info didn't have a value destructor, but the value inserted into
it was copied with tp_asv_set_boxed; in addition, the original value
wasn't freed either.

Reviewed-by: Senko Rasic <da5bfd2d8145dba298faec38e53dbf4456eb0394@collabora.co.uk>

freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control