wireprotohelpers: add missing b prefixes

# skip-blame just b prefixes

Differential Revision: https://phab.mercurial-scm.org/D4254

tests/wireprotohelpers.sh

@@ -20,19 +20,19 b' from mercurial import ('
     wireprotov2server,
 )
 
[e-mail]('customreadonly', permission='pull')
[e-mail](b'customreadonly', permission=b'pull')
 def customreadonlyv1(repo, proto):
     return wireprototypes.bytesresponse(b'customreadonly bytes response')
 
[e-mail]('customreadonly', permission='pull')
[e-mail](b'customreadonly', permission=b'pull')
 def customreadonlyv2(repo, proto):
     return wireprototypes.cborresponse(b'customreadonly bytes response')
 
[e-mail]('customreadwrite', permission='push')
[e-mail](b'customreadwrite', permission=b'push')
 def customreadwrite(repo, proto):
     return wireprototypes.bytesresponse(b'customreadwrite bytes response')
 
[e-mail]('customreadwrite', permission='push')
[e-mail](b'customreadwrite', permission=b'push')
 def customreadwritev2(repo, proto):
     return wireprototypes.cborresponse(b'customreadwrite bytes response')
 EOF