Simplify YangInstanceIdentifier references

Now that the (binding) InstanceIdentifier and YangInstanceIdentifier
have different names, we can import both at the same time, clarifying a
bit the code.

Change-Id: I270f2eac40c4e94eb2a61b604657bcfa28a9b3cd
Signed-off-by: Robert Varga <rovarga@cisco.com>
Merge "Simplify YangInstanceIdentifier references"