Remove test_execfile (#1049)

Author: slozier

Src/IronPythonTest/Cases/IronPythonCasesManifest.ini

@@ -40,9 +40,6 @@ IsolationLevel=PROCESS # required to have quit/exit
 Ignore=true
 Reason=This one needs a lot of work to use unittest (if it even can)
 
-[IronPython.test_execfile]
-Ignore=true
-
 [IronPython.test_fuzz_parser]
 Ignore=true
 Reason=Takes way too long (ran overnight without completing!)