Bug 1759030 - Use 'verifications' from upstream taskgraph module, r=releng-reviewers,gbrown

This is the last place that in `gecko_taskgraph/generator.py` that calls into
`gecko_taskgraph` code. By removing it, the two generator.py files will be
identical and the `gecko_taskgraph` copy can be removed.

Differential Revision: https://phabricator.services.mozilla.com/D161080

taskcluster/gecko_taskgraph/__init__.py

@@ -50,6 +50,12 @@ def register(graph_config):
     from gecko_taskgraph import (  # noqa: trigger target task method registration
         target_tasks,
     )
+    from gecko_taskgraph import generator
     from gecko_taskgraph import morph  # noqa: trigger morph registration
+    from gecko_taskgraph.util.verify import verifications
+
+    # Don't use the upstream verifications, and replace them with our own.
+    # TODO Investigate merging our verifications with upstream.
+    generator.verifications = verifications
 
     register_parameters()

taskcluster/gecko_taskgraph/generator.py

@@ -18,8 +18,7 @@ from taskgraph.taskgraph import TaskGraph
 from taskgraph.transforms.base import TransformSequence, TransformConfig
 from taskgraph.util.python_path import find_object
 from taskgraph.util.yaml import load_yaml
-
-from .util.verify import verifications
+from taskgraph.util.verify import verifications
 
 logger = logging.getLogger(__name__)