Replace unneeded module_implements()/function() pattern with module_invoke_all

In IRC aspilicious mentioned #1220830-1: Minor performance improvement for _hs_taxonomy_hierarchical_select_terms_to_options() which moves the module_exists call outside of the foreach to save function calls.

I double checked the code base, and all of the module_exists are outside loops, as well as all but one of the module_implements calls.

The one that was in a loop turns out to be completely unnecessary, since the reason for it was removed here http://drupalcode.org/project/fullcalendar.git/blobdiff/ce76580..8b9eb10...