fix(build): switch to cjs output for es5.

System output does not work at the current versions of TS and
system.js. Will revisit after upgrading TS.

Removes unused traceur tooling.

Closes #3974

modules/examples/e2e_test/sourcemap/sourcemap_spec.ts

@@ -34,15 +34,10 @@ describe('sourcemaps', function() {
 
       var originalPosition = decoder.originalPositionFor({line: errorLine, column: errorColumn});
 
-      var finalMapData = fs.readFileSync('dist/js/prod/es6/examples/src/sourcemap/index.js.map');
-      var finalDecoder = new sourceMap.SourceMapConsumer(JSON.parse(finalMapData));
-
-      var finalPosition = finalDecoder.originalPositionFor(originalPosition);
-
       var sourceCodeLines =
           fs.readFileSync('modules/examples/src/sourcemap/index.ts', {encoding: 'UTF-8'})
               .split('\n');
-      expect(sourceCodeLines[finalPosition.line - 1])
+      expect(sourceCodeLines[originalPosition.line - 1])
           .toMatch(/throw new BaseException\(\'Sourcemap test\'\)/);
     });
   });