ANDROID: usb: f_accessory: Remove stale comments

Neither acc_gadget_bind() nor acc_gadget_register_driver() exist, so
remove the stale comments that refer to them.

Bug: 173789633
Signed-off-by: Will Deacon <willdeacon@google.com>
Change-Id: If396ba3bcac3ca59c48e5a5faa0a8520534ed625
Signed-off-by: Giuliano Procida <gprocida@google.com>