[css mode] Remove support for SGML-style comments

Closes #3244

mode/css/css.js

@@ -653,16 +653,6 @@ CodeMirror.defineMode("css", function(config, parserConfig) {
     return ["comment", "comment"];
   }
 
-  function tokenSGMLComment(stream, state) {
-    if (stream.skipTo("-->")) {
-      stream.match("-->");
-      state.tokenize = null;
-    } else {
-      stream.skipToEnd();
-    }
-    return ["comment", "comment"];
-  }
-
   CodeMirror.defineMIME("text/css", {
     documentTypes: documentTypes,
     mediaTypes: mediaTypes,
@@ -674,11 +664,6 @@ CodeMirror.defineMode("css", function(config, parserConfig) {
     colorKeywords: colorKeywords,
     valueKeywords: valueKeywords,
     tokenHooks: {
-      "<": function(stream, state) {
-        if (!stream.match("!--")) return false;
-        state.tokenize = tokenSGMLComment;
-        return tokenSGMLComment(stream, state);
-      },
       "/": function(stream, state) {
         if (!stream.eat("*")) return false;
         state.tokenize = tokenCComment;

mode/css/test.js

@@ -76,13 +76,6 @@
   MT("tagTwoPropertiesURL",
      "[tag foo] { [property background]: [atom url]([string //example.com/foo.png]); [property padding]: [number 0]; }");
 
-  MT("commentSGML",
-     "[comment <!--comment-->]");
-
-  MT("commentSGML2",
-     "[comment <!--comment]",
-     "[comment -->] [tag div] {}");
-
   MT("indent_tagSelector",
      "[tag strong], [tag em] {",
      "  [property background]: [atom rgba](",