exec: Weaken dumpability for secureexec

commit e816c201aed5232171f8eb80b5d46ae6516683b9 upstream.

This is a logical revert of commit e37fdb78 ("exec: Use secureexec
for setting dumpability")

This weakens dumpability back to checking only for uid/gid changes in
current (which is useless), but userspace depends on dumpability not
being tied to secureexec.

  https://bugzilla.redhat.com/show_bug.cgi?id=1528633



Reported-by: Tom Horsley <horsley1953@gmail.com>
Fixes: e37fdb78 ("exec: Use secureexec for setting dumpability")
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>