Move test cases from 'tests/ghc-regress' to 'tests'

[David Terei]

Hi All,

I've been doing some work on the testsuite recently and developed a
minor annoyance. The test cases all reside in 'tests/ghc-regress'. The
'tests' directory itself only contains the single, 'ghc-regress'
folder so it feel useless. Is there a good reason for this layout? Can
we get ride of it and just have all the test cases reside directly in
'tests'. Think of all the cumulative time that we would save not
having to type out the full path or press tab anymore!

Cheers,
David