playlist: use uri_has_scheme() instead of isRemoteUrl()

For internal checks (i.e. not in command.c), we need to check whether
an URI is in the databse, in the local file system or a remote URI
with a scheme.

src/playlist.c

@@ -565,7 +565,7 @@ song_by_url(const char *url)
 	if (song != NULL)
 		return song;
 
-	if (isRemoteUrl(url))
+	if (uri_has_scheme(url))
 		return song_remote_new(url);
 
 	return NULL;