Macaron: remove custom Request type (#37874)

* remove macaron.Request, use http.Request instead

* remove com dependency from bindings module

* fix another c.Req.Request

pkg/services/ngalert/api/api_alertmanager.go

@@ -372,7 +372,7 @@ func (srv AlertmanagerSrv) RoutePostTestReceivers(c *models.ReqContext, body api
 
 	ctx, cancelFunc, err := contextWithTimeoutFromRequest(
 		c.Req.Context(),
-		c.Req.Request,
+		c.Req,
 		defaultTestReceiversTimeout,
 		maxTestReceiversTimeout)
 	if err != nil {