Fix big memory leak when relying on View#remove to cleanup

Since a single/global viewMethods was previously used to store event hashes,
if you were done with a view and only relied on View#remove
(since https://github.com/Codecademy/backbone.declarative/pull/3)
for cleanup rather than calling unbindXEvents manually, then even if you disposed
of all of your own view references, Backbone Declarative's viewMethods variable would
hold a reference to each event method which, by closure, would contain the
View itself.