cocoa: do not enable coreaudio automatically

Remove the automagic connection between --enable-cocoa
and enabling coreaudio in audio_drv_list.  It can be
overridden anyway just by placing --enable-cocoa before
--audio-drv-list.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -1149,9 +1149,7 @@ for opt do
   ;;
   --disable-cocoa) cocoa="disabled"
   ;;
-  --enable-cocoa)
-      cocoa="enabled" ;
-      audio_drv_list="coreaudio $(echo $audio_drv_list | sed s,coreaudio,,g)"
+  --enable-cocoa) cocoa="enabled"
   ;;
   --disable-system) softmmu="no"
   ;;