Move the signature tests from cambridge suite to CompilerComent tests

[KevinRansom]

While reviewing a recent PR that added a new signature test to the cambridge suite I noticed that:

fsharp/tests/fsharp/tests.fs

Line 3340 in f9c5b42

module GeneratedSignatureTests =

1. The small suite of signature tests run on the desktop clr only. They run on the desktop because they invoke the compiler with the results of building the sig file
2. They would work fine in one of the better test frameworks we have.

We should move these tests away from the crazy place that is the cambridge suite :-)