Bug 1519310 - Remove NSS_DISABLE_LIBPKIX. r=dmajor

It was used to disable libpkix in NSS when NSS was built with its
Makefiles, but it's now built with gyp, and this knob does nothing.
The equivalent is the gyp variable disable_libpkix, which is set in
security/moz.build.

Depends on D16285

Differential Revision: https://phabricator.services.mozilla.com/D16286

--HG--
extra : moz-landing-system : lando

old-configure.in

@@ -3821,10 +3821,6 @@ HAVE_SYS_MOUNT_H
 # Avoid using obsolete NSPR features
 AC_DEFINE(NO_NSPR_10_SUPPORT)
 
-# Don't build NSS libpkix
-NSS_DISABLE_LIBPKIX=1
-AC_SUBST(NSS_DISABLE_LIBPKIX)
-
 MOZ_CREATE_CONFIG_STATUS()
 
 unset MAKEFILES