proc: just list_del() struct pde_opener

list_del_init() is too much, structure will be freed in three lines
anyway.

Link: http://lkml.kernel.org/r/20161029155313.GA1246@avx2


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