MAINTAINERS: remove sthemmin

Leaving Microsoft, the Hyper-V drivers have lots of other maintainers.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Link: https://lore.kernel.org/r/20221028153741.25470-1-stephen@networkplumber.org


Signed-off-by: Wei Liu <wei.liu@kernel.org>