[RFC][lit] Renaming "python-psutil" feature

Hi All,

The current implementation of lit test timeouts needs the python psutil module to kill a process tree after a timeout. The lit feature “python-psuti” is used to indicate when it is present.

I’m currently working on removing this dependency on the AIX platform where psutil doesn’t work well (https://reviews.llvm.org/D64251).

I’d like to propose renaming the feature to “lit-max-individual-test-time”, as some platforms now won’t require psutil to implement this behaviour and this better reflects what is actually being required.

As far as I am aware the feature is only currently used in lit’s own test suite (though external tests could be utilizing it).