Remove finalization from JDBC classes

[mrotteveel]

Currently, Jaybird performs finalization at two places: JDBC classes (FBConnection and FBStatement), and within GDS-ng (various classes). Given finalization is deprecated for removal, it is a good idea to try and get rid of it. As a first step, removal from the JDBC classes makes sense as this basically doubles for the finalization that occurs with GDS-ng.

Usage within GDS-ng will probably need to be replaced with a cleaner (though some usages might be removable as well), but we cannot do that until we stop supporting Java 8.