HiveServer2: Cleanup code which checks for ThriftJDBCSerde usage

As part of HIVE-14039, we simplified the condition checking by setting a boolean in SessionState (from HiveSessionImpl) and then using that in other layers to decide whether we should use ThriftJDBCSerde. However, there are some parts of the code (e.g. FileSinkOperator.closeOp, Driver.getResults, SQLOperation.getNextRowSet) where the condition checking is still complicated - we should refactor that.