Drop Oracle/Sun compiler from CI tests?

[giacomofiorin]

Developer Studio is a commercial compiler that back in the day used to provide informative warning messages. However, it has a few caveats:

• Restrictive license forces us to use secrets in CI; we're already doing that for NAMD and VMD, but the fewer the better.
• Does not support anything more recent than C++11, and there seem to be no plans to change that.
• The logic of its warnings about function hiding (one of its most useful IMO) starts getting a bit fragile when both virtual and override are used in the same class (even if not on the same function).

Open source tools like clang-tidy provide a useful alternative, especially if one fine-tunes their scope to avoid it being too aggressive.

Thoughts?

[jhenin]

I see no problem with dropping it.