chore: drop mention of Python 2.7 from templates (#252)

Source-Link: googleapis/synthtool@facee4c
Post-Processor: gcr.io/repo-automation-bots/owlbot-python:latest@sha256:9743664022bd63a8084be67f144898314c7ca12f0a03e422ac17c733c129d803

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: gcf-owl-bot[bot]

.github/.OwlBot.lock.yaml

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

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