[PATCH] Remove event swallower engravers/translators

[Neil Puttock]

Hi everybody,

While puzzling over the purpose of the method try_music (), I noticed
that the only engravers/translators to use this method are the type
swallowers/Swallow_engraver/performer.  Since this method appears to
have been junked when the translator listener macros were introduced
for stream events, none of these translators serves any useful
purpose.  Furthermore, all events are either listened to (in at least
one engraver/performer) or explicitly declared as unlistened (e.g.,
HarmonicEvent), so there's no need to silence them: they no longer
generate `event junked' warnings.

I've posted a patch on Rietveld which removes the following translators:

Note_swallow_translator
Rest_swallow_translator
Skip_event_swallow_translator
String_number_engraver
Swallow_engraver
Swallow_performer

Please review here: http://codereview.appspot.com/174085

Regards,
Neil