Remove unnecessary checks for encrypted types

Remove unnecessary checks for encrypted types

Change I6ba62a58ac62a3b7bfb2b9d4d18b37ef458b616c makes it unnecessary
to explicitly check that a volume is encrypted prior to invoking the
volume_encryption_metadata_get function. This change cleans up the
single existing invocation of that function in the API contrib
modules. The unit tests are also updated to reflect this change.

Change-Id: I3b8aef67bd6e70f570a39c90175ae6ceaedc4386