Proposal: remove XpressProblem class (keep XPRESS solver support!)

[rileyjmurray]

We have a class called XpressProblem defined in cvxpy/problems/xpress_problem.py. This class is basically dead code. From what I can tell, it's only used in one place, and that place is an odd example: examples/advanced/xpress_example.py.

I'd like for CVXPY 1.4 to mark this class as deprecated with a notice that it's slated for removal in CVXPY 1.5. I know that this could in principle be a breaking change, but I seriously doubt that it will affect anyone.

@cvxpy/maintainers, what do you think?

[SteveDiamond]

Sounds good to me.

[phschiele]

@rileyjmurray agree with your proposal and playing it safe. While it could be breaking, it is also not part of the public API.

[rileyjmurray]

... we didn't get around to doing this, did we?

Ping @phschiele and @SteveDiamond