mm: remove activate_page() from unuse_pte()

We don't initially add anon pages to active lruvec after commit
b518154e ("mm/vmscan: protect the workingset on anonymous LRU").
Remove activate_page() from unuse_pte(), which seems to be missed by the
commit.  And make the function static while we are at it.

Before the commit, we called lru_cache_add_active_or_unevictable() to add
new ksm pages to active lruvec.  Therefore, activate_page() wasn't
necessary for them in the first place.

Signed-off-by: Yu Zhao <yuzhao@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: Alexander Duyck <alexander.h.duyck@linux.intel.com>
Cc: Huang Ying <ying.huang@intel.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Qian Cai <cai@lca.pw>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
Link: http://lkml.kernel.org/r/20200818184704.3625199-1-yuzhao@google.com


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>