Remove compatibility macros m4_ifblank and m4_ifnblank

They are at least since Autoconf 2.67 present,
and we are requiring version 2.69.

Change-Id: I41b33d4ebe02198f03cdddcc4a3c1beedd993d78
Signed-off-by: R. Diez <rdiezmail-openocd@yahoo.de>
Reviewed-on: http://openocd.zylin.com/6239
Tested-by: jenkins
Reviewed-by: Antonio Borneo <borneo.antonio@gmail.com>

config_subdir.m4

@@ -1,17 +1,3 @@
-dnl
-dnl If needed, define the m4_ifblank and m4_ifnblank macros from autoconf 2.64
-dnl This allows us to run with earlier Autoconfs as well.
-ifdef([m4_ifblank],[],[
-m4_define([m4_ifblank],
-[m4_if(m4_translit([[$1]],  [ ][	][
-]), [], [$2], [$3])])])
-dnl
-ifdef([m4_ifnblank],[],[
-m4_define([m4_ifnblank],
-[m4_if(m4_translit([[$1]],  [ ][	][
-]), [], [$3], [$2])])])
-dnl
-
 dnl AC_CONFIG_SUBDIRS does not allow configure options to be passed
 dnl to subdirs, this function allows that by creating a configure.gnu
 dnl script that prepends configure options and then calls the real