Remove two dummied-out dependencies from Travis

One isn't used anymore, and the other isn't relevant to this branch

.travis.yml

@@ -38,8 +38,6 @@ addons:
         - libsdl2-dev
         - libfreetype6-dev
         - libfltk1.3-dev
-#        - libglew-dev # Needed by OpenGL renderer
-#        - libxmp-dev  # Needed by AUDIO_TRACKER in the enhanced branch
   homebrew:
     packages:
         - cmake
@@ -48,8 +46,6 @@ addons:
         - sdl2
         - freetype
         - fltk
-#        - glew
-#        - libxmp-lite
     update: true
 
 env: