Revert "fix E403 'Package installs should not use latest'"

This reverts commit bcfe1cbd.

Broken.

    fatal: [matrix.archlinux.org]: FAILED! => {"changed": false, "msg": "value of state must be one of: present, absent, latest, forcereinstall, got: 1.14.0"}

roles/matrix/defaults/main.yml

----
-matrix_pip_version: 1.14.0

roles/matrix/tasks/main.yml

@@ -33,7 +33,7 @@
     name:
       - 'matrix-synapse[postgres,systemd,url_preview]'
       - pip
-    state: "{{ matrix_pip_version }}"
+    state: latest
     extra_args: '-U --upgrade-strategy=eager'
     virtualenv: /var/lib/synapse/venv
   become: yes