fetch2: Correct the clean() mechanism for the fetcher2 code

This create a clean() method in each of the fetcher modules
and correctly cleans the .done stamp file and lock files

Signed-off-by: Saul Wold <sgw@linux.intel.com>

bitbake/lib/bb/fetch2/local.py

@@ -74,3 +74,7 @@ class Local(FetchMethod):
         if os.path.exists(urldata.localpath):
             return True
         return False
+
+    def clean(self, urldata, d):
+        return
+