walkchangerevs: simplify by using match.always() method

Since "slowpath = match.anypats() or (match.files() and
opts.get('removed'))", we can simplify the condition "not slowpath and
not match.files()" to "not match.anypats() and not match.files()",
which is equivalent to "match.always()".

mercurial/cmdutil.py

@@ -1698,7 +1698,7 b' def walkchangerevs(repo, match, opts, pr'
     # wanted: a cache of filenames that were changed (ctx.files()) and that
     # match the file filtering conditions.
 
-    if not slowpath and not match.files():
+    if match.always():
         # No files, no patterns.  Display all revs.
         wanted = revs