Revert "ppp: Fix throttling bugs"

This reverts commit a6540f73

, as
requested by Alan:

  "... as it was wrong, the pty code is now fixed and the fact this
   isn't reverted is breaking pptp setups."

Requested-by: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>