sched: remove INIT_COMPLETION

All users are converted over to reinit_completion(). Remove the old
macro now.

Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>