MAINTAINERS: Change Solarflare maintainers

Email from solarflare.com will stop working. Update the maintainers.
A replacement for linux-net-drivers@solarflare.com is not working yet,
for now remove it.

Signed-off-by: Martin Habets <mhabets@solarflare.com>
Signed-off-by: Edward Cree <ecree@solarflare.com>
Link: https://lore.kernel.org/r/20201120113207.GA1605547@mh-desktop


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