debugutils: skip "parent" property for elements when dumping pipeline graph

debugutils: skip "parent" property for elements when dumping pipeline graph

Seems unnecessary to print the parent name for every
element in the pipeline graph, it's clear from the
graph what the parent element is and it's hard to
imagine a case where this is useful info rather than
just distracting spam. So far this was only done for
pads, but we should just do it for everything.