main/postmarketos-ui-mate: remove pavucontrol
After PulseAudio support for MATE sound was enabled in Alpine Linux, its interfaces are now available in the native MATE sound settings. The additional PulseAudio volume control application therefore became redundant.
I didn't bump "pkgrel", I think it's not necessary for changes on "_pmb_recommends"?
For the record, MR and commit in Alpine Linux (they somehow got deteched):