Renamed all methods called delete to remove

This is because Internet Explorer <= 8 has `delete` as a reserved keyword that you cannot name your methods

test/backend.elasticsearch.test.js

@@ -220,7 +220,7 @@ test("write", function() {
       equal(data._version, 2);
 
       // delete
-      var jqxhr = backend.delete(rec.id);
+      var jqxhr = backend.remove(rec.id);
       jqxhr.done(function(data) {
         ok(data.ok);
         rec = null;

test/backend.memory.test.js

@@ -135,7 +135,7 @@ test('update and delete', function () {
   equal(data.data[0].x, newVal);
 
   // Test Delete
-  data.delete(doc1);
+  data.remove(doc1);
   equal(data.data.length, 5);
   equal(data.data[0].x, memoryData[1].x);
 });