tests: remove the global G_LOG_DOMAIN to avoid issues with including code from elsewhere

including wp/spa-props.c currently re-defines G_LOG_DOMAIN
in the spa-props.c unit test

tests/wp/meson.build

@@ -5,7 +5,6 @@ common_env = [
 ]
 common_args = [
   '-DG_LOG_USE_STRUCTURED',
-  '-DG_LOG_DOMAIN="test"',
 ]
 
 test(