Fixed prefixFieldClashes for TextFormatter and added coverage

formatter.go

@@ -34,15 +34,18 @@ func prefixFieldClashes(data Fields, fieldMap FieldMap) {
 	timeKey := fieldMap.resolve(FieldKeyTime)
 	if t, ok := data[timeKey]; ok {
 		data["fields."+timeKey] = t
+		delete(data, timeKey)
 	}
 
 	msgKey := fieldMap.resolve(FieldKeyMsg)
 	if m, ok := data[msgKey]; ok {
 		data["fields."+msgKey] = m
+		delete(data, msgKey)
 	}
 
 	levelKey := fieldMap.resolve(FieldKeyLevel)
 	if l, ok := data[levelKey]; ok {
 		data["fields."+levelKey] = l
+		delete(data, levelKey)
 	}
 }