revert: remove sysusers uid/gid pin

This reverts commit 68bb560. The pinned users (pipewire, rtkit, wsdd) are
created by the base image layers before this drop-in is applied, and
systemd-sysusers never renumbers existing users, so the pin was a no-op
against the inherited gid 970/969 collisions. The collision is harmless
(no files are owned by the shared gids and audio limits resolve by name),
so we accept it rather than carry an ineffective file.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: KernelFreeze