Deprecate the AMP warnings.

Now that we're in development mode, Applicative will soon be a
superclass of Monad in HEAD. So let's go ahead and deprecate the
-fno-warn-amp flag, remove the checks, and tweak a few tests

Signed-off-by: Austin Seipp <austin@well-typed.com>
testsuite/spec001: untabify, kill trailing whitespace

Signed-off-by: Austin Seipp <austin@well-typed.com>