runtime/pprof: expect tests to pass on macOS

macOS tests have been disabled since CL 12429045 (Aug 2013).
At the time, macOS required a kernel patch to get a working profiler
(https://research.swtch.com/macpprof), which we didn't want
to require, of course.

macOS has improved - it no longer requires the kernel patch - but
we never updated the list of exceptions.

As far as I can tell, the builders have no problem passing the pprof test now.
(It is possible that the iOS builders have trouble, but that is now a different GOOS.)

Remove the exception for macOS. The test should now pass.

Fixes #6047.

Change-Id: Iab49036cacc1025e56f515bd19d084390c2f5357
Reviewed-on: https://go-review.googlesource.com/c/go/+/292229


Trust: Russ Cox <rsc@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>