Remove virtual source to mirror changes from Valve

See e734a2227f an an explanation.

system_files/deck/shared/usr/etc/pipewire/virtual-source.conf

@@ -1,17 +0,0 @@
-context.modules = [
-    {   name = libpipewire-module-loopback
-        args = {
-            node.name = virtual-source
-            node.description = "Virtual Source"
-            capture.props = {
-                audio.position = [ FL FR ]
-                stream.dont-remix = true
-                node.passive = true
-            }
-            playback.props = {
-                audio.position = [ FL FR ]
-                media.class = Audio/Source
-            }
-        }
-    }
-]