Remove excess methods from GtidSet

The binary log reader library has a GtidSet class that it uses to track the GTIDs appearing in the binlog. However, this class didn't provide methods to compare different instances, which our MySQL connector requires to compare offsets (e.g., in database history). The MySQL connector added its own GtidSet class that emulated (and accepted in the constructor) the library's GtidSet and provided this missing functionality. It also added a few convenience methods used in the unit tests.

Recently, we contributed our comparison logic to the MySQL Binlog Connector Java library, and this was accepted recently.

Since we may want to eventually migrate to or have our GtidSet wrap the com.github.shyiko.mysql.binlog.GtidSet, we should remove the convenience methods.