docs: do not mention EGL_MESA_drm_display

This extension was removed back in 2016, but it seems we left a mention
of it in the docs.

The entire section with this extension seems kinda pointless now, so
let's drop it entirely.

Fixes: f3e23ead53 ("egl: remove remnants of MESA_drm_display")
Reviewed-by: David Heidelberg <david.heidelberg@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19719>
(cherry picked from commit 9f2c9e4c3f)

.pick_status.json

@@ -499,7 +499,7 @@
         "description": "docs: do not mention EGL_MESA_drm_display",
         "nominated": true,
         "nomination_type": 1,
-        "resolution": 0,
+        "resolution": 1,
         "main_sha": null,
         "because_sha": "f3e23ead536e66940053265216b3886fef69d891"
     },

docs/egl.rst

@@ -90,12 +90,6 @@ at runtime
    the main library uses the first platform listed in
    ``-D platforms=...`` as the native platform.
 
-   Extensions like ``EGL_MESA_drm_display`` define new functions to
-   create displays for non-native platforms. These extensions are
-   usually used by applications that support non-native platforms.
-   Setting this variable is probably required only for some of the demos
-   found in mesa/demo repository.
-
 ``EGL_LOG_LEVEL``
    This changes the log level of the main library and the drivers. The
    valid values are: ``debug``, ``info``, ``warning``, and ``fatal``.