Remove redundant, failing, test
Remove redundant, failing, test

This test didn't do what it claimed to do, and what it claimed to do was the
same as test_cant_hide_direct_ancestors anyway.

This stuff is tested by sytest anyway.

matrix-org/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse,matrix-org/synapse