MAINTAINERS: remove myself as a VKMS maintainer

I haven't been able to follow or review the work on the driver for some
time now and I don't see the situation improving anytime soon. I'd like
to continue being listed as a reviewer.

Signed-off-by: Melissa Wen <melissa.srw@gmail.com>
Acked-by: Maíra Canal <mcanal@igalia.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240525142637.82586-1-melissa.srw@gmail.com