Remove support for vprof

[bouweandela]

The vprof package is no longer maintained, so it would be good to remove support for it.

[bouweandela]

@ESMValGroup/esmvaltool-developmentteam Does anyone use the profile_diagnostic setting? If not, we can probably remove the feature completely.

If there is an interest in keeping the feature, we could switch to a maintained profiler such as py-spy.

[ehogan]

No; we purposefully don't install vprof at the MO as it's not available via conda-forge 👍