refactor: remove 'hgmo' template for taskgraph init

hg.mozilla.org is being decommissioned and new repos will no longer be
created there. Besides, this template never worked and had a bunch of
errors in it.

Author: ahal

src/taskgraph/main.py

@@ -912,16 +912,14 @@ def init_taskgraph(options):
 
     if repo.tool == "git" and "github.com" in repo_url:
         context["repo_host"] = "github"
-    elif repo.tool == "hg" and "hg.mozilla.org" in repo_url:
-        context["repo_host"] = "hgmo"
     else:
         print(
             dedent(
                 """\
             Repository not supported!
 
-            Taskgraph only supports repositories hosted on Github or hg.mozilla.org.
-            Ensure you have a remote that points to one of these locations.
+            The `taskgraph init` command only supports repositories hosted on
+            Github. Ensure you use a remote that points to a Github repository.
             """
             ),
             file=sys.stderr,

template/cookiecutter.json

@@ -1,7 +1,7 @@
 {
     "project_name": "my-project",
     "taskgraph_version": "{{ cookiecutter.taskgraph_version }}",
-    "repo_host": ["github", "hgmo"],
+    "repo_host": ["github"],
     "repo_name": "my-repo",
     "project_slug": "{{ cookiecutter.repo_name.lower().replace(' ', '_').replace('-', '_') }}",
     "trust_domain": "mozilla",

template/{{cookiecutter.project_name}}/taskcluster.hgmo.yml

@@ -263,10 +263,15 @@ def test_init_taskgraph(mocker, tmp_path, project_root, repo_with_upstream):
     oldcwd = Path.cwd()
     try:
         os.chdir(repo_root)
-        taskgraph_main(["init", "--template", str(project_root)])
+        ret = taskgraph_main(["init", "--template", str(project_root)])
     finally:
         os.chdir(oldcwd)
 
+    if repo.tool == "hg":
+        assert ret == 1
+        assert not (repo_root / ".taskcluster.yml").exists()
+        return
+
     # Make assertions about the repository state.
     expected_files = [
         ".taskcluster.yml",