MDL-33774 mod_label stores the content where it is supposed to

removed hardcoded checking for 'label' module type
MDL-33774 instead of checking that activity is label we check that it has view url
MDL-33774 filter_activitynames removed hardcoded label module type
Revert "MDL-33774 filter_activitynames removed hardcoded label module type"

This reverts commit 91494bdf09cccceda797ff27bfff0afa08585d53.