gbm: remove unnecessary meson include

`inc_wayland_drm` is only used if wayland is built, and it's already
added in that case a few lines below.

Fixes: a29869e8 "gbm: Don't traverse backwards for includes"
Signed-off-by: Eric Engestrom <eric.engestrom@intel.com>
Reviewed-by: Emil Velikov <emil.velikov@collabora.com>
Reviewed-by: Dylan Baker <dylan@pnwbakers.com>
(cherry picked from commit 7df80de6)