Fold MainVarsWrapper
It does not make any sense to keep a separate object to keep
state, while YangInstanceIdentifierDeserializer is pure static.
Eliminate MainVarsWrapper as a separate subclass, encapsulating
it in an YangInstanceIdentifierDeserializer instead. This allows
us manipulate state data freely, without having to go through
accessors, and thus make it much easier to follow as to what is
happening.
Change-Id: Ifa241c7343e13fe524ad8cf7d05cb3a6bbd6a18b
Signed-off-by: Robert Varga <robert.varga@pantheon.tech>