[FIX] .travis.yml: Remove of old wkhtmltopdf refs

.travis.yml

@@ -7,20 +7,12 @@ python:
 
 addons:
   apt:
-    sources:
-      - pov-wkhtmltopdf
     packages:
       - expect-dev  # provides unbuffer utility
       - python-lxml  # because pip installation is slow
       - python-simplejson
       - python-serial
       - python-yaml
-      - wkhtmltopdf
-
-# set up an X server to run wkhtmltopdf.
-before_install:
-  - "export DISPLAY=:910.0"
-  - "sh -e /etc/init.d/xvfb start"
 
 env:
   global: