MAINTAINERS: trim the GVE entry

We requested in the past that GVE patches coming out of Google should
be submitted only by GVE maintainers. There were too many patches
posted which didn't follow the subsystem guidance.

Recently Joshua was added to maintainers, but even tho he was asked
to follow the netdev "FAQ" in the past [1] he does not follow
the local customs. It is not reasonable for a person who hasn't read
the maintainer entry for the subsystem to be a driver maintainer.

We can re-add once Joshua does some on-list reviews to prove
the fluency with the upstream process.

Link: https://lore.kernel.org/20240610172720.073d5912@kernel.org # [1]
Link: https://patch.msgid.link/20250215162646.2446559-1-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>