[Transform] Allow project_routing

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/transform/transforms/TransformConfig.java

@@ -387,13 +387,6 @@ ActionRequestValidationException validateNoCrossProjectWhenCrossProjectFeatureIs
                     validationException
                 );
             }
-            // verify there is no project routing
-            if (getSource().getProjectRouting() != null) {
-                validationException = addValidationError(
-                    "Cross-project calls are not supported, but project_routing was requested: " + getSource().getProjectRouting(),
-                    validationException
-                );
-            }
         }
         return validationException;
     }

x-pack/plugin/core/src/test/java/org/elasticsearch/xpack/core/transform/transforms/TransformConfigTests.java

@@ -1139,10 +1139,6 @@ public void testCrossProjectWithFeatureDisabled() throws IOException {
             validationException.getMessage(),
             containsString("Cross-project calls are not supported, but remote indices were requested: [project-1:src]")
         );
-        assertThat(
-            validationException.getMessage(),
-            containsString("Cross-project calls are not supported, but project_routing was requested: _alias:_origin")
-        );
     }
 
     public void testNotCrossProjectEnvironment() throws IOException {