Remove need for hack

We're way past the version of codemirror to need this hack.

Change-Id: Ie0c034832329ecf734229c521dbf3397d925a387

gr-editor/gr-editor.js

diff --git a/gr-editor/gr-editor.js b/gr-editor/gr-editor.js
index c88e2a8..caf00d0 100644
--- a/gr-editor/gr-editor.js
+++ b/gr-editor/gr-editor.js
@@ -95,12 +95,6 @@
   return link;
 }
 
-// we need to be on codemirror 5.33.0+ to get the support for
-// text/x-php in CodeMirror.findModeByMIME
-const LANGUAGE_MAP = {
-  'text/x-php': 'php',
-};
-
 class GrEditor extends Polymer.Element {
   /**
    * Fired when the content of the editor changes.
@@ -233,7 +227,7 @@
    * @returns {string}
    */
   _mapFileType(type) {
-    return LANGUAGE_MAP[type] || type || '';
+    return type || '';
   }
 }