proc: remove MODULE_LICENSE

proc is not modular, so MODULE_LICENSE just expands to empty space.  proc
without doubts remains GPLed.

Signed-off-by: Alexey Dobriyan <adobriyan@sw.ru>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>