mm/page_ext.c: drop pfn_present() check when onlining

mm/page_ext.c: drop pfn_present() check when onlining

Since commit c5e79ef561b0 ("mm/memory_hotplug.c: don't allow to
online/offline memory blocks with holes") we disallow to offline any
memory with holes.  As all boot memory is online and hotplugged memory
cannot contain holes, we never online memory with holes.

This present check can be dropped.

Signed-off-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Anshuman Khandual <anshuman.khandual@arm.com>
Cc: Dan Williams <dan.j.williams@intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Pavel Tatashin <pasha.tatashin@soleen.com>
Cc: "Rafael J. Wysocki" <rafael@kernel.org>
Link: http://lkml.kernel.org/r/20200127110424.5757-4-david@redhat.com
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>