Revert "Add error to SessionExist interface"

This reverts commit 28e6b3b924.

session/couchbase/sess_couchbase.go

@@ -179,16 +179,16 @@ func (cp *Provider) SessionRead(sid string) (session.Store, error) {
 
 // SessionExist Check couchbase session exist.
 // it checkes sid exist or not.
-func (cp *Provider) SessionExist(sid string) (bool, error) {
+func (cp *Provider) SessionExist(sid string) bool {
 	cp.b = cp.getBucket()
 	defer cp.b.Close()
 
 	var doc []byte
 
 	if err := cp.b.Get(sid, &doc); err != nil || doc == nil {
-		return false, err
+		return false
 	}
-	return true, nil
+	return true
 }
 
 // SessionRegenerate remove oldsid and use sid to generate new session