MAINTAINERS: Remove Keith from NVDIMM maintainers

I no longer work in this capacity for the NVDIMM or DAX subsystems.
Signed-off-by: Keith Busch <kbusch@kernel.org>
Link: https://lore.kernel.org/r/20191122162644.27078-1-kbusch@kernel.orgSigned-off-by: Dan Williams <dan.j.williams@intel.com>

MAINTAINERS

@@ -4879,7 +4879,6 @@ F:	include/trace/events/fs_dax.h
 DEVICE DIRECT ACCESS (DAX)
 M:	Dan Williams <dan.j.williams@intel.com>
 M:	Vishal Verma <vishal.l.verma@intel.com>
-M:	Keith Busch <keith.busch@intel.com>
 M:	Dave Jiang <dave.jiang@intel.com>
 L:	linux-nvdimm@lists.01.org
 S:	Supported
@@ -9336,7 +9335,6 @@ LIBNVDIMM: NON-VOLATILE MEMORY DEVICE SUBSYSTEM
 M:	Dan Williams <dan.j.williams@intel.com>
 M:	Vishal Verma <vishal.l.verma@intel.com>
 M:	Dave Jiang <dave.jiang@intel.com>
-M:	Keith Busch <keith.busch@intel.com>
 M:	Ira Weiny <ira.weiny@intel.com>
 L:	linux-nvdimm@lists.01.org
 Q:	https://patchwork.kernel.org/project/linux-nvdimm/list/