MAINTAINERS: Remove Shannon Nelson from MAINTAINERS file

Brett Creeley is taking ownership of AMD/Pensando drivers while I wander
off into the sunset with my retirement this month.  I'll still keep an
eye out on a few topics for awhile, and maybe do some free-lance work in
the future.

Meanwhile, thank you all for the fun and support and the many learning
opportunities :-).

Special thanks go to DaveM for merging my first patch long ago, the big
ionic patchset a few years ago, and my last patchset last week.

Redirect things to a non-corporate account.

Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Brett Creeley <brett.creeley@amd.com>
Link: https://patch.msgid.link/20250616224437.56581-1-shannon.nelson@amd.com


[Jakub: squash in the .mailmap update]
Signed-off-by: Shannon Nelson <sln@onemain.com>
Link: https://patch.msgid.link/20250619010603.1173141-1-sln@onemain.com


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