MAINTAINERS: remove myself as maintainer of SMC

I changed responsibilities some time ago, its time
to remove myself as maintainer of the SMC component.

Signed-off-by: Karsten Graul <kgraul@linux.ibm.com>
Signed-off-by: Wenjia Zhang <wenjia@linux.ibm.com>
Link: https://lore.kernel.org/r/20231207202358.53502-1-wenjia@linux.ibm.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: karstengr

MAINTAINERS

@@ -19638,7 +19638,6 @@ S:	Maintained
 F:	drivers/misc/sgi-xp/
 
 SHARED MEMORY COMMUNICATIONS (SMC) SOCKETS
-M:	Karsten Graul <kgraul@linux.ibm.com>
 M:	Wenjia Zhang <wenjia@linux.ibm.com>
 M:	Jan Karcher <jaka@linux.ibm.com>
 R:	D. Wythe <alibuda@linux.alibaba.com>