staging: wilc1000: remove wilc_strutils.c and wilc_strutils.h

Remove wilc_strutils.c and wilc_strutils.h that are not needed.
wilc_strutils.o is also removed in Makefile.

Signed-off-by: Chaehyun Lim <chaehyun.lim@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>