fs/proc/array.c: delete children_seq_release()

It is 1:1 wrapper around seq_release().

Link: http://lkml.kernel.org/r/20171122171510.GA12161@avx2


Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Acked-by: Cyrill Gorcunov <gorcunov@openvz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>