travis: drop stale devkitPro-cache

The new pacman-based devkitPro installer is so fast that there's
really no point in caching here, it takes more time to download the
cache than to reinstall.

.travis.yml

@@ -2,10 +2,6 @@ language: c
 
 sudo: false
 
-cache:
-  directories:
-    - $HOME/devkitPro
-
 install:
   - wget https://github.com/devkitPro/pacman/releases/download/devkitpro-pacman-1.0.1/devkitpro-pacman.deb &&
     sudo dpkg -i devkitpro-pacman.deb