Clean static/index.html.
Clean static/index.html.

Sorry for not rebasing (no features changed).
It almost pass w3c's Nu Html Checker.

mattgodbolt/compiler-explorer,dkm/gcc-explorer,mattgodbolt/compiler-explorer,mattgodbolt/gcc-explorer,ibuclaw/gcc-explorer,mattgodbolt/gcc-explorer,dkm/gcc-explorer,mattgodbolt/gcc-explorer,dkm/gcc-explorer,mattgodbolt/compiler-explorer,dkm/gcc-explorer,ibuclaw/gcc-explorer,mattgodbolt/compiler-explorer,mattgodbolt/compiler-explorer,mattgodbolt/compiler-explorer,dkm/gcc-explorer,ibuclaw/gcc-explorer,mattgodbolt/compiler-explorer,dkm/gcc-explorer,mattgodbolt/compiler-explorer,ibuclaw/gcc-explorer,dkm/gcc-explorer,ibuclaw/gcc-explorer,dkm/gcc-explorer,dkm/gcc-explorer,mattgodbolt/gcc-explorer,mattgodbolt/gcc-explorer