Remove obsolete visualization section.

[hjoliver]

This is a small change with no associated Issue. Partially addresses #3379. May c-l-o-s-e #3696 (final check needed, of that umbrella issue).

• remove obsolete [visualization] config section.
  • future Cylc 8 viz config will be different. The old config was very much tailored for graphviz.
• simplify get_graph_raw() which was keeping track of family collapse state for the old UI. It now has a single argument to specify which families to collapse, and does not remember the collapsed state
• modify cylc graph and cylc list, and functional tests that use them, accordingly (slightly enhanced too: they can take an interval for the stop point).

The PR would have been a lot smaller if I'd retained [visualization]initial/final cycle point which was being used by most of the functional tests that use cylc graph --reference ... but, better to remove the whole [visualization] section now. flow.cylc should define the whole graph, and cylc graph etc. should just specify what part of it they want to see.

Requirements check-list

• I have read CONTRIBUTING.md and added my name as a Code Contributor.
• Contains logically grouped changes (else tidy your branch by rebase).
• Does not contain off-topic changes (use other PRs for other changes).
• Applied any dependency changes to both setup.py and conda-environment.yml. [None]
• Already covered by existing tests. (Removed some [vis] tests)
• (master branch) I have opened a documentation PR at Remove obsoletion flow.cylc visualization section. cylc-doc#253

[hjoliver]

Draft while I fix tests that use visualization settings to define the graph extent.

[hjoliver]

@oliver-sanders maybe one review will do as this is mostly functional test tweaks. Assign another reviewer if you like though.

[wxtim]

Very likely that this closes #3696 - after this has gone in that will need a final check, and can then be closed... 🎉

[hjoliver]

Very likely that this closes #3696 - after this has gone in that will need a final check, and can then be closed... tada

Good spotting @wxtim - I'll update the description above.

[visualization] -> obsolete

[wxtim]

• read it
• tried it on random local workflows.

[oliver-sanders]

Moved the milestone forward on #3696