Feature: libpe_status: drop hack to support old GUI

Could affect manipulation of old CIBs created by the original pacemaker GUI
back when it couldn't create meta-attributes (or other old CIBs that similarly
put meta-attributes in the instance attributes, with a crm_feature_set before
3.0.9).

Also update affected regression tests (which is probably the only reason this
support wasn't completely removed earlier).