Remove only first matching tag

Current implementation would fail when iterating on the next
element, looking for tags to remove as we changed the underlying
collection. Stopping on first occurence is a fine workaround.

rnsutils/instrument.py

@@ -223,6 +223,7 @@ class RenoiseInstrument(object):
             tag = self.root.GlobalProperties.Tags.Tag[tag_idx]
             if tag.text == tag_to_remove:
                 del self.root.GlobalProperties.Tags.Tag[tag_idx]
+                return
 
     def cleanup(self):
         # ensure that key mapping remains in the limits of what renoise supports