We stopped testing these configurations a while ago, and it doesn't
really make sense to allow nodes to run in this configuration. This
drops support for non-blocksync nodes and cleans up the
configuration/tests accordingly.
Closes: #6908
This tweaks the connectivity of test configurations, in hopes that more will be viable.
Additionally reduces the prevalence of testing the legacy mempool.
A few notes:
- this is not all the deletion that we can do, but this is the most
"simple" case: it leaves in shims, and there's some trivial
additional cleanup to the transport that can happen but that
requires writing more code, and I wanted this to be easy to review
above all else.
- This should land *after* we cut the branch for 0.35, but I'm
anticipating that to happen soon, and I wanted to run this through
CI.
