Remove Phoenix 6 references in mostrobotpy

[daltzctr]

I believe this is breaking mid-season, so probably a merge for post season. We have had several customers get bit by robotpy installing an out-of-date Phoenix 6 vendordep with critical fixes or changes that can't be traced down to a pinned dependency. This is due to the implicit pinning of versions in the robotpy_extras block.

Our recommendation is to just add the phoenix6 dependency to the

requires = [

]

block anyways. Python handles this correctly during both sync and deploy.

[virtuald]

Yeah, I'd like to remove it: robotpy/robotpy-installer#118

For this season, I think it would be best to just bump the version or expand the dependency range.