Remove SDL from android image

.travis.yml

@@ -64,7 +64,6 @@ addons:
     - libgstreamer-plugins-base1.0-dev
     - libgstreamer1.0-0:amd64
     - libgstreamer1.0-dev
-    - libsdl2-dev
     - libudev-dev
     - wget
 
@@ -81,6 +80,11 @@ before_install:
         export JOBS=$((`sysctl -n hw.ncpu`+1));
     fi
 
+  # Linux needs sdl2 but not android
+  - if [ "${SPEC}" = "linux-g++-64" ]; then
+        sudo apt-get install -y libsdl2-dev;
+    fi
+
 install:
   # linux dependencies: qt
   - if [ "${SPEC}" = "linux-g++-64" ]; then