fix($sanitize): reduce stack height

Update Internet Explorer-only helper function stripCustomNsAttrs to be less
recursive. Reduce stack height of function causing out of stack space error.

Closes angular#14928

Author: Bob Chao

test/ngSanitize/sanitizeSpec.js

@@ -134,14 +134,12 @@ describe('HTML', function() {
     // Large is non-trivial to quantify, but handling 100,000 should be sufficient for most purposes.
     var largeNumber = 100000; // 100,000
     var element = '<div>b</div>';
-    var largeDataset = '';
     var result = '';
     // Ideally we would use repeat, but that isn't supported in IE.
     for (var i = 0; i < largeNumber; i++) {
-      largeDataset += element;
       result += element;
     }
-    expectHTML('a' + largeDataset + 'c').toEqual('a' + result + 'c');
+    expectHTML('a' + result + 'c').toEqual('a' + result + 'c');
   });
 
   it('should remove style', function() {