DCD-386: Remove use of amazon-linux-extras command as it breaks in a clean virtualenv; psql isn't actually used, and can be installed manually if needed.

roles/product_common/tasks/amazon.yml

@@ -10,9 +10,3 @@
   yum:
     name:
       - dejavu-fonts-common  # Required by the installer
-
-# Amazon Linux 2 supplies extra packages via a special command.
-- name: Enable Postgresql from 'extras'
-  command: amazon-linux-extras install -y "postgresql{{ postgres_version }}"
-  args:
-    creates: /usr/bin/psql

roles/product_common/tasks/ubuntu.yml

@@ -11,5 +11,4 @@
 - name: Install other base packages on Ubuntu
   package:
     name:
-      - postgresql-client
       - fonts-dejavu-core  # Required by installer