config: remove the stream from the default endpoint-link files

So that we can use media.role to specify the stream

src/wireplumber/default-input-audio.endpoint-link

@@ -6,7 +6,6 @@ media_class = "Stream/Input/Audio"
 [target-endpoint]
 media_class = "Audio/Source"
 streams = "default.streams"
-stream = "Multimedia"
 properties = [
   { name = "api.alsa.path", value = "hw:0,0" },
 ]

src/wireplumber/default-output-audio.endpoint-link

@@ -6,7 +6,6 @@ media_class = "Stream/Output/Audio"
 [target-endpoint]
 media_class = "Audio/Sink"
 streams = "default.streams"
-stream = "Multimedia"
 properties = [
   { name = "api.alsa.path", value = "hw:0,0" },
 ]