MAINT: cleanup all `from_name` usage in tests

[bsipocz]

We should try to limit the unnecessary use of SkyCoord.from_name in the tests and just use baked in numbers for coordinates instead. That would remove some unnecessary extra calls to upstream that we don't need to test for (e.g. astropy should have enough coverage to ensure from_name just works).

Narrative docs is different IMO as the from_name is a really nice end user functionality, so we can keep promoting its usage.