Remove unused imports

There are several imports that are not used.  Remove them.

Change-Id: I2ac3be66827bd68d3faedcef7d6bbf30ea01d3f2
diff --git a/manifest_xml.py b/manifest_xml.py
index 26cc14f..205e4af 100644
--- a/manifest_xml.py
+++ b/manifest_xml.py
@@ -20,7 +20,7 @@
 import urlparse
 import xml.dom.minidom
 
-from git_config import GitConfig, IsId
+from git_config import GitConfig
 from project import RemoteSpec, Project, MetaProject, R_HEADS, HEAD
 from error import ManifestParseError