remove pubspec.lock (#6208)

Author: wing328

pom.xml

@@ -1392,7 +1392,7 @@
                 <module>samples/openapi3/client/petstore/ruby</module>
                 <!-- test java-related projects -->
                 <module>samples/openapi3/client/petstore/scala-akka</module>
-                <!--<module>samples/client/petstore/dart2/petstore</module>-->
+                <module>samples/client/petstore/dart2/petstore</module>
                 <module>samples/client/petstore/dart-jaguar/openapi</module>
                 <module>samples/client/petstore/dart-jaguar/flutter_petstore/openapi</module>
                 <module>samples/client/petstore/scala-httpclient</module>