x86/mm: Drop deprecated DISCONTIGMEM support for 32-bit

The DISCONTIGMEM support was marked as deprecated in v5.2 and since there
were no complaints about it for almost 5 releases it can be completely
removed.

Signed-off-by: Mike Rapoport <rppt@linux.ibm.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lkml.kernel.org/r/20200223094322.15206-1-rppt@kernel.org

arch/x86/include/asm/pgtable_32.h

@@ -66,8 +66,7 @@ do {						\
 #endif /* !__ASSEMBLY__ */
 
 /*
- * kern_addr_valid() is (1) for FLATMEM and (0) for
- * SPARSEMEM and DISCONTIGMEM
+ * kern_addr_valid() is (1) for FLATMEM and (0) for SPARSEMEM
  */
 #ifdef CONFIG_FLATMEM
 #define kern_addr_valid(addr)	(1)