Fix install of libpq-dev and python-psycopg2 via APT instead of pip

tasks/install-requirements.yml

@@ -2,10 +2,6 @@
 
 - name: Installation des dépendances pour HedgeDoc
   apt:
-    name: ['postgresql','nodejs','git','npm','yarn','bash','nginx']
+    name: ['postgresql','nodejs','git','npm','yarn','bash','nginx','python-psycopg2','libpq-dev']
     state: present
     update_cache: yes
-
-- name: Installation de la dépendance python
-  pip:
-    name: psycopg2