[locomotiv] Session frees node annotations on destruction (#3441)

[locomotiv] Session frees node annotations on destruction (#3441)

* [locomotiv] Session frees node annotations on destruction

This commit introduces destructor of Session. Previously node
annotations set by Session, like NodeDataImpl, remain even after
Session closed. They were not memory leak by definition, as they can
be accessed through another Session. However node annotations maybe
preserved until program ends, so it is like memory leak. This commit
would prevent that situation.

Signed-off-by: Cheongyo Bahk <ch.bahk@samsung.com>
* Delete unused using Index

* Session is final class