RubyArray keeps references to unreachable RubyObjects after clear, reject!, delete and delete_at

RubyArrays don't explicitly dereference elements that are removed for Array#clear and leave extra references to other elements in the backing values array as the elements are shifted about in the reject!, delete and delete_at implementations. This causes memory leaks in our application as we rely on Array#clear and Array#delete(_at|_if) to remove references to objects so they may be collected.

Attached is a patch that removes unneeded references to RubyObjects in RubyArray's values array for clear, reject!, delete and delete_at. The patch also includes 4 java unit tests; there is one test for each method which assert invalidated values entries are set to null.