Cleanup NamespaceStorageSupport/StmtContext API conflict
StmtContext has a few methods that are logically implemented by
NamespaceStorageSupport. Since NamespaceStorageSupport does not
implements StmtContext (nor should it), these methods happen to
work as they overlap with StmtContextBase's mixin -- and they
cannot be simply found by looking for implementations.
Resolve the naming conflict in the most logical way, thus improving
quality of life for everyone :)
Change-Id: I0186a94699c5945b7140bf57ba9e5900e49019d4
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>