Khronos stopped supporting .spec files in 2013. They're now over a year
old without support. As such it's not worth us continuing to support
them either.
Signatures were split into 4 APIs before (gl, glcore, gles1, gles2).
However, gles2 contains bindings for both version 2.0 and 3.0. The
version information is now maintained, which allows us to cut down on
the number of generated enumerations.
GLXmlParser now explicitly marks its output with version="2", while
the older .spec parsers produce version="1" signatures. The binding
generator uses the newer API to support multiple apinames in the same
file.