Revert "Merge branch 'public-sdl2-update' into 'master'"

libs/SDL2/COPYING.txt

libs/SDL2/Makefile

libs/SDL2/SRB2NOTE.txt

libs/SDL2/WhatsNew.txt

libs/SDL2/docs/README-android.md

libs/SDL2/docs/README-dynapi.md

libs/SDL2/docs/README-raspberrypi.md

libs/SDL2/docs/README-winrt.md

libs/SDL2/i686-w64-mingw32/bin/SDL2.dll

libs/SDL2/i686-w64-mingw32/bin/sdl2-config

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL.h

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL_assert.h

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL_atomic.h

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL_audio.h

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL_bits.h

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL_blendmode.h

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL_clipboard.h

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL_config.h

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL_cpuinfo.h

libs/SDL2/i686-w64-mingw32/include/SDL2/SDL_egl.h