perf: add two more missing b prefixes for Python 3

# skip-blame just two more b prefixes

Differential Revision: https://phab.mercurial-scm.org/D5425

contrib/perf.py

@@ -1021,10 +1021,10 b' def perfindex(ui, repo, **opts):'
     opts = _byteskwargs(opts)
     timer, fm = gettimer(ui, opts)
     mercurial.revlog._prereadsize = 2**24 # disable lazy parser in old hg
-    if opts['rev'] is None:
+    if opts[b'rev'] is None:
         n = repo[b"tip"].node()
     else:
-        rev = scmutil.revsingle(repo, opts['rev'])
+        rev = scmutil.revsingle(repo, opts[b'rev'])
         n = repo[rev].node()
 
     unfi = repo.unfiltered()