Fix promises-aplus testcfg.py

Fix GetSourceForTest which returned an incorrect result.
With this fix promises-aplus shows correct sources when --cat option is specified.

BUG=
R=jkummerow@chromium.org

Review URL: https://codereview.chromium.org/258763002

Patch from Yutaka Hirano <yhirano@chromium.org>.

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@21026 ce2b1a6d-e550-0410-aec6-3dcde31c8c00

test/promises-aplus/testcfg.py

@@ -85,7 +85,6 @@ class PromiseAplusTestSuite(testsuite.TestSuite):
   def GetSourceForTest(self, testcase):
     filename = os.path.join(self.root, TEST_NAME,
                             'lib', 'tests', testcase.path + '.js')
-    return 'print("FAIL: fail");'
     with open(filename) as f:
       return f.read()