Minor cleanups in get_fcov.py

[rswarbrick]

Avoid importing some stuff that we're not using. Break a long line. No functional change.

[rswarbrick]

Hmm, I think @hcallahan-lowrisc remembers that these were actually needed for some library to work properly. We should probably fix things or at least add a documentation comment, but I'm not exactly sure what was going on! So I'm closing this for now: we can always tidy it up later.

[hcallahan-lowrisc]

I just tried this now to see if I remembered it right. If you remove the import, you get the following traceback:
(I removed it in compile_tb.py, but the outcome would be the same)

  File "dv/uvm/core_ibex/scripts/compile_tb.py", line 110, in <module>
    sys.exit(_main())
  File "dv/uvm/core_ibex/scripts/compile_tb.py", line 51, in _main
    with LockedMetadata(args.dir_metadata, __file__) as md:
  File "dv/uvm/core_ibex/scripts/metadata.py", line 496, in __enter__
    self.md = pickle.load(self.handle)
AttributeError: Can't get attribute 'RegressionMetadata' on <module '__main__' from 'dv/uvm/core_ibex/scripts/compile_tb.py'>

This seems to be something strange to do with re-loading the pickled file. At a glance, I'm out of ideas!