Another left-over from ancient module code, it was supposed to return
non-zero if the module has a use count, but currently it always
evaluates to 0.

There are a few users of different types:
(1)  ioctl that perform a while(MOD_IN_USE) MOD_DEC_USE_COUNT loop.
     Just rip them out, we now have forced module unloading.
(2)  printk's that moan if the use-count in not zero in the exitfunc.
     Just rip them out, this can't happen.
(3)  if(MOD_IN_USE) MOD_DEC_USE_COUNT constructs in ->close of a few
     serial drivers.  Just remove the conditional, we did a
     MOD_INC_USE_COUNT in ->open.
(4)  This one is interesting:  drivers/sbus/char/display7seg.c uses
     the module use count to track openers.  Replace this with an
     atomic_t.

In addition remove tons of stale comments in network driver that aren't
understandable for anyone who doesn't know ancient Linux module semantics.