egl: drop confusing mincore() error message

egl: drop confusing mincore() error message

A user came to me asking how to fix this error, but it's entirely
expected that `get_wl_surface_proxy()` on recent enough wayland
compositors will always print it.
Let's just remove the message altogether, it is basically never useful.

Reviewed-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3219>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/merge_requests/3219>