mm: remove dummy struct bootmem_data/bootmem_data_t

Both bootmem_data and bootmem_data_t structures are no longer defined.
Remove the dummy forward declarations.
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Baoquan He <bhe@redhat.com>
Acked-by: Mike Rapoport <rppt@linux.ibm.com>
Link: http://lkml.kernel.org/r/20200326022617.26208-1-longman@redhat.comSigned-off-by: Linus Torvalds <torvalds@linux-foundation.org>

arch/alpha/include/asm/mmzone.h

@@ -8,8 +8,6 @@
 
 #include <asm/smp.h>
 
-struct bootmem_data_t; /* stupid forward decl. */
-
 /*
  * Following are macros that are specific to this numa platform.
  */

include/linux/mmzone.h

@@ -664,7 +664,6 @@ struct deferred_split {
  * Memory statistics and page replacement data structures are maintained on a
  * per-zone basis.
  */
-struct bootmem_data;
 typedef struct pglist_data {
 	struct zone node_zones[MAX_NR_ZONES];
 	struct zonelist node_zonelists[MAX_ZONELISTS];