MAINTAINERS: drop separate x86/mm section

Let the subtree fall under general x86 maintainership instead, then also
properly reflecting Roger's role there.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Roger Pau Monné <roger.pau@citrix.com>

MAINTAINERS

@@ -594,12 +594,6 @@ F:	tools/misc/xen-cpuid.c
 F:	tools/tests/cpu-policy/
 F:	tools/tests/x86_emulator/
 
-X86 MEMORY MANAGEMENT
-M:	Jan Beulich <jbeulich@suse.com>
-M:	Andrew Cooper <andrew.cooper3@citrix.com>
-S:	Supported
-F:	xen/arch/x86/mm/
-
 X86 MEMORY PAGING
 S:	Orphaned
 F:	xen/arch/x86/mm/mem_paging.c