revert "selftest: add simple test for soft-dirty bit"

Revert commit 58c7be84 ("selftest: add simple test for soft-dirty
bit").  This is the self test for Pavel's pagemap2 patches which didn't
actually get merged.

Reported-by: Pavel Emelyanov <xemul@parallels.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>