chore: drop mention of Python 2.7 from templates

.github/.OwlBot.lock.yaml

@@ -1,3 +1,3 @@
 docker:
   image: gcr.io/repo-automation-bots/owlbot-python:latest
-  digest: sha256:a1a891041baa4ffbe1a809ac1b8b9b4a71887293c9101c88e8e255943c5aec2d
+  digest: sha256:9743664022bd63a8084be67f144898314c7ca12f0a03e422ac17c733c129d803

noxfile.py

@@ -84,9 +84,15 @@ def default(session):
     constraints_path = str(
         CURRENT_DIRECTORY / "testing" / f"constraints-{session.python}.txt"
     )
-    session.install("asyncmock", "pytest-asyncio", "-c", constraints_path)
-
-    session.install("mock", "pytest", "pytest-cov", "-c", constraints_path)
+    session.install(
+        "mock",
+        "asyncmock",
+        "pytest",
+        "pytest-cov",
+        "pytest-asyncio",
+        "-c",
+        constraints_path,
+    )
 
     session.install("-e", ".", "-c", constraints_path)
 

scripts/readme-gen/templates/install_deps.tmpl.rst

@@ -12,7 +12,7 @@ Install Dependencies
    .. _Python Development Environment Setup Guide:
        https://cloud.google.com/python/setup
 
-#. Create a virtualenv. Samples are compatible with Python 2.7 and 3.4+.
+#. Create a virtualenv. Samples are compatible with Python 3.6+.
 
     .. code-block:: bash