log: make "slowpath" condition slightly more readable

Before 8e0e334bad42 and 6c76c42a5893, the condition was "anypats() or
(files() and --removed)". This can be read as "<match is actually slow>
or <walk files including removed revs>". So "not always()" (i.e. walk
file revs) seems more appropriate here.

The logic should be unchanged:

  not anypats() => always() or isexact() or prefix()
  isexact()     => not always()
  prefix()      => not always()

mercurial/cmdutil.py

@@ -2193,8 +2193,7 b' def walkchangerevs(repo, match, opts, pr'
     if not revs:
         return []
     wanted = set()
-    slowpath = match.anypats() or ((match.isexact() or match.prefix()) and
-                                   opts.get('removed'))
+    slowpath = match.anypats() or (not match.always() and opts.get('removed'))
     fncache = {}
     change = repo.changectx
 
@@ -2390,8 +2389,7 b' def _makelogrevset(repo, pats, opts, rev'
     # platforms without shell expansion (windows).
     wctx = repo[None]
     match, pats = scmutil.matchandpats(wctx, pats, opts)
-    slowpath = match.anypats() or ((match.isexact() or match.prefix()) and
-                                   opts.get('removed'))
+    slowpath = match.anypats() or (not match.always() and opts.get('removed'))
     if not slowpath:
         for f in match.files():
             if follow and f not in wctx: