revert "proc: fix the threaded proc self"

revert "proc: fix the threaded proc self"

Revert commit c6caeb7c4544608e8ae62731334661fc396c7f85 ("proc: fix the
threaded /proc/self"), since Eric says "The patch really is wrong.
There is at least one corner case in procps that cares."

Cc: Eric W. Biederman <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: "Guillaume Chazarain" <[email protected]>
Cc: "Pavel Emelyanov" <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Oleg Nesterov <[email protected]>
Cc: Roland McGrath <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>