d2e8bc4499 was the the commit that
originally introduced the usage of this bit. As the message states, the
purpose was to force creating GLES 3 contexts on drivers that do not
return a higher version context than what was requested. With the recent
opengl refactors, mpv's gl selection has already moved away from such
complicated queries. Perhaps when that commit was added things were
different, but nowadays it seems like Mesa simply returns the highest
driver version available that is compatibile with the request (i.e.
requesting GLES 2 returns a GLES 3 context on my machine). In that case,
let's just simply drop EGL_OPENGL_ES3_BIT altogether as it does break
GLES 2 only machines. Fixes#9431.
c478a1efba