egl: fix libdrm-less builds

This function was never used, and isn't properly guarded by HAVE_LIBDRM,
breaking the build on systems that don't have libdrm.

Let's just remove it.

Fixes: 7552fcb7 "egl: add base EGL_EXT_device_base implementation"
Reported-by: Timo Aaltonen <tjaalton@debian.org>
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Acked-by: Emil Velikov <emil.velikov@collabora.com>
(cherry picked from commit bcc4bfc8)