selftests: kselftest: Remove outdated comment

Commit 3c07aaef ("selftests: kselftest: change KSFT_SKIP=4 instead of
KSFT_PASS") reverted commit 11867a77 ("selftests: kselftest framework:
change skip exit code to 0") but missed removing the comment which that
commit added, so do that now.

Signed-off-by: Thiago Jung Bauermann <bauerman@linux.ibm.com>
Signed-off-by: Shuah Khan (Samsung OSG) <shuah@kernel.org>