Remove the "If only executable code is distributed..." paragraph from
the license text. Everything now uses a normal MIT license.
The only code from Khronos that's included in libglvnd is the EGL/GL
header and XML files, which do not contain that paragraph.
Fixes https://gitlab.freedesktop.org/glvnd/libglvnd/-/issues/221
Added a test for EGL_EXT_device_enumeration and EGL_EXT_platform_device, plus
dispatching to an EGL extesnion function based on an EGLDeviceEXT handle.