Travis: Remove conflicting postgresql versions again

.travis.yml

@@ -41,18 +41,15 @@ script:
 addons:
   # test with last version that still supports OIDs
   postgresql: "11"
-  apt:
-    packages:
-    - postgresql-11
-    - postgresql-client-11
 
 services:
   - postgresql
 
 before_script:
   - sudo service postgresql stop
+  - sudo apt-get remove -y postgresql\*
+  - sudo apt-get install postgresql-11 postgresql-client-11
   - sudo -u postgres sed -i "s/port = 54[0-9][0-9]/port = 5432/" /etc/postgresql/11/main/postgresql.conf
   - sudo service postgresql start 11
-  - sudo cat /etc/postgresql/11/main/pg_hba.conf
   - sudo -u postgres psql -c 'create database unittest'