travis: remove no longer needed libudev-dev dependency

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Axel Davy <axel.davy@ens.fr>
Reviewed-by: Nicolai Hähnle <nicolai.haehnle@amd.com>
diff --git a/.travis.yml b/.travis.yml
index 5f489a4..3d107aa 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -11,7 +11,6 @@
   apt:
     packages:
       - libdrm-dev
-      - libudev-dev
       - x11proto-xf86vidmode-dev
       - libexpat1-dev
       - libxcb-dri2-0-dev