BUG-865: removed unused utility methods from SchemaContextUtil

By using getOriginal method from DerivableSchemaNode we can avoid searching for original node from grouping. This causes
that some of utility methods from SchemaContextUtil become redundant.

Change-Id: I96e2832436331b2f454e21aedb01fb552e2e2d6e
Signed-off-by: Martin Vitez <mvitez@cisco.com>
BUG-1377: fixed code generation for nodes defined under grouping.

If node was defined in choice case which parent choice was defined in grouping,
node does not implement ChildOf interface. Fixed by adding search for parent node
also from groupings.

Added test.

Change-Id: Ibfbb4deb719804fd16cce5c091cc0969aeaf821e
Signed-off-by: Martin Vitez <mvitez@cisco.com>
Merge changes Ibfbb4deb,I96e28324

* changes:
  BUG-1377: fixed code generation for nodes defined under grouping.
  BUG-865: removed unused utility methods from SchemaContextUtil