remove the watcher interface

Author: shogo82148

driver.go

@@ -23,11 +23,6 @@ import (
 	"sync"
 )
 
-// watcher interface is used for context support (From Go 1.8)
-type watcher interface {
-	startWatcher()
-}
-
 // MySQLDriver is exported to make the driver directly accessible.
 // In general the driver is used via the database/sql package.
 type MySQLDriver struct{}
@@ -96,9 +91,7 @@ func (d MySQLDriver) Open(dsn string) (driver.Conn, error) {
 	}
 
 	// Call startWatcher for context support (From Go 1.8)
-	if s, ok := interface{}(mc).(watcher); ok {
-		s.startWatcher()
-	}
+	mc.startWatcher()
 
 	mc.buf = newBuffer(mc.netConn)