Since CL 33071, testCPUProfile is only one user of the badOS map.
Replace it by the corresponding switch, with the "plan9" case removed
because it is already checked earlier in the same function.

Change-Id: Id647b8ee1fd37516bb702b35b3c9296a4f56b61b
Reviewed-on: https://go-review.googlesource.com/75110
Run-TryBot: Tobias Klauser <tobias.klauser@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>