sdl: UNBUILDABLE Remove SDL 1.3 in prep for SDL 2.0 pull.

Removing SDL altogether ties off the 1.3 history so that it doesn't
muddy the 2.0 history moving forward.
sdl: UNBUILDABLE Initial commit SDL 2.0 from upstream.

Source: http://hg.libsdl.org/SDL
Changeset: 7025 (4eb8ac58642c)
build: UNBUILDABLE Update makefile dependencies from SDL=>SDL2.
sdl: UNBUILDABLE Use GLES2 instead of GLES1.
build: UNSTABLE Remove front-end, gles2n64, gles2rice from build.

Emulator will not run without front-end, but app now builds.

Just renamed the makefiles so that these modules won't be compiled.
Allows build to succeed so that we can work out the upgrade kinks one
module at a time.