QA: remove moderated notion from collape tests

The scenario "For a moderated post, a mode cycle with no user override
keeps it hidden" is obsolete and is breaking.
"first non-moderated topic" doesn't apply, so remove its elements and
reuse the existing flow_first_topic page elements.

Also remove obsolete "who started the first topic", we removed that line
in the titlebar some time ago.

All tests pass in Firefox against ee-flow

Bug: 73451

Change-Id: I8a2e197c5f3b4751531f0ffc27d497a0f947284f
Merge "QA: remove moderated notion from collape tests"