Revert "ValueTracking: Identify implied fp classes by general fcmp (#66505)"

This causes asserts to fire:

  llvm/lib/Analysis/ValueTracking.cpp:4262:
  std::tuple<Value *, FPClassTest, FPClassTest> llvm::fcmpImpliesClass(CmpInst::Predicate, const Function &, Value *, const APFloat *, bool):
  Assertion `(RHSClass == fcPosNormal || RHSClass == fcNegNormal || RHSClass == fcPosSubnormal || RHSClass == fcNegSubnormal) && "should have been recognized as an exact class test"' failed.

See comments on the PR.

> Previously we could recognize exact class tests performed by
> an fcmp with special values (0s, infs and smallest normal).
> Expand this to recognize the implied classes by a compare with a general
> constant. e.g. fcmp ogt x, 1 implies positive and non-0.
>
> The API should be better merged with fcmpToClassTest but that
> made the diff way bigger, will try to do that in a future
> patch.

This reverts commit dc3faf0e.