media: Remove transport owner list
media: Remove transport owner list

Transports now have zero or one owners, so there is no need to maintain
a list any more.

ComputeCycles/bluez,pstglia/external-bluetooth-bluez,ComputeCycles/bluez,silent-snowman/bluez,pkarasev3/bluez,pstglia/external-bluetooth-bluez,mapfau/bluez,pkarasev3/bluez,silent-snowman/bluez,pkarasev3/bluez,silent-snowman/bluez,pstglia/external-bluetooth-bluez,mapfau/bluez,pkarasev3/bluez,ComputeCycles/bluez,silent-snowman/bluez,pstglia/external-bluetooth-bluez,ComputeCycles/bluez,mapfau/bluez,mapfau/bluez