upgrade: rename UPGRADE_FILELOG to UPGRADE_FILELOGS

They are multiple filelog to upgrade, so this seems more accurate.

Differential Revision: https://phab.mercurial-scm.org/D9466

mercurial/upgrade.py

@@ -716,10 +716,10 b' def _copyrevlog(tr, destrepo, oldrl, une'
 
 UPGRADE_CHANGELOG = object()
 UPGRADE_MANIFEST = object()
-UPGRADE_FILELOG = object()
+UPGRADE_FILELOGS = object()
 
 UPGRADE_ALL_REVLOGS = frozenset(
-    [UPGRADE_CHANGELOG, UPGRADE_MANIFEST, UPGRADE_FILELOG]
+    [UPGRADE_CHANGELOG, UPGRADE_MANIFEST, UPGRADE_FILELOGS]
 )
 
 
@@ -753,7 +753,7 b' def matchrevlog(revlogfilter, entry):'
         return UPGRADE_CHANGELOG in revlogfilter
     elif entry.endswith(b'00manifest.i'):
         return UPGRADE_MANIFEST in revlogfilter
-    return UPGRADE_FILELOG in revlogfilter
+    return UPGRADE_FILELOGS in revlogfilter
 
 
 def _clonerevlogs(