Description

This PR moves 2 x blocks of code to use switch statements for a bit more clarity, as suggested by the gocritic linter. Also the .NewGoMySQLReader() func of go/binlog/gomysql_reader.go was simplified (unused err removed, etc)

This change should result in the exact same behaviour as before

Details:

1. Simplify .NewGoMySQLReader() func in go/binlog/gomysql_reader.go
   • Remove unused err return
2. Use a type-based switch for binlog event type in go/binlog/gomysql_reader.go
   • This simplifies a future PR for GTID support
3. Use switch on the CutOverType field to pick cutover logic

• contributed code is using same conventions as original code
• script/cibuild returns with no formatting errors, build errors or unit test errors