Remove disabling group seek bar for devices group

With ag/33996857, devices without group volume control support won't be
collapsed, so there is no need to disable the group seek bar.

Test: atest
Bug: 385672684
Flag: com.android.media.flags.enable_output_switcher_personal_audio_sharing

Change-Id: I43c5d816aea2b4bd9b78343708d1fa40e9ed82a0