removed SDL libraries in preparation for tracking the official mercurial repos with git subtree and git-remote-hg
Squashed 'android/jni/SDL_mixer/' content from commit c9f51a2

git-subtree-dir: android/jni/SDL_mixer
git-subtree-split: c9f51a216cca7d8ef3b59a6b60caa5ffe273978a
Merge commit '5636040ec07188ec5010a343133eb747bc2f49c9' as 'android/jni/SDL_mixer'
Squashed 'android/jni/SDL/' content from commit a367fb3

git-subtree-dir: android/jni/SDL
git-subtree-split: a367fb39c56120a30f0661d5c47cef7b89743451
Merge commit '77b4bd73440c7b60fdc085d96744bd8d519d9d96' as 'android/jni/SDL'
fix build