Remove image-url function signature

This was deprecated a long time ago!

Author: mgreter

src/functions.cpp

@@ -1719,17 +1719,6 @@ namespace Sass {
       return res;
     }
 
-    ////////////////
-    // URL FUNCTIONS
-    ////////////////
-
-    Signature image_url_sig = "image-url($path, $only-path: false, $cache-buster: false)";
-    BUILT_IN(image_url)
-    {
-      error("`image_url` has been removed from libsass because it's not part of the Sass spec", pstate);
-      return 0; // suppress warning, error will exit anyway
-    }
-
     //////////////////////////
     // MISCELLANEOUS FUNCTIONS
     //////////////////////////

src/functions.hpp

@@ -89,7 +89,6 @@ namespace Sass {
     extern Signature call_sig;
     extern Signature not_sig;
     extern Signature if_sig;
-    extern Signature image_url_sig;
     extern Signature map_get_sig;
     extern Signature map_merge_sig;
     extern Signature map_remove_sig;
@@ -172,7 +171,6 @@ namespace Sass {
     BUILT_IN(call);
     BUILT_IN(sass_not);
     BUILT_IN(sass_if);
-    BUILT_IN(image_url);
     BUILT_IN(map_get);
     BUILT_IN(map_merge);
     BUILT_IN(map_remove);