Revert "patch deletion in codemirror"

This reverts commit 331a5f7fe85a6e894c35b64cd7987ed53f59ea57.

IPython/frontend/html/notebook/static/codemirror/lib/codemirror.js

@@ -2194,20 +2194,6 b' var CodeMirror = (function() {'
       cm.indentLine(cm.getCursor().line);
     },
     toggleOverwrite: function(cm) {cm.toggleOverwrite();}
-    ,delSpaceToPrevTabStop : function(cm){
-        var from = cm.getCursor(true), to = cm.getCursor(false), sel = !posEq(from, to);
-        if (!posEq(from, to)) {cm.replaceRange("", from, to); return}
-        var cur = cm.getCursor(), line = cm.getLine(cur.line);
-        var tabsize = cm.getOption('tabSize');
-        var chToPrevTabStop = cur.ch-(Math.ceil(cur.ch/tabsize)-1)*tabsize;
-        var from = {ch:cur.ch-chToPrevTabStop,line:cur.line}
-        var select = cm.getRange(from,cur)
-        if( select.match(/^\ +$/) != null){
-            cm.replaceRange("",from,cur)
-        } else {
-            cm.deleteH(-1,"char")
-        }
-    }
   };
 
   var keyMap = CodeMirror.keyMap = {};