hgk: remove a "b" used on a kwargs expansion, the keys are strs

Differential Revision: https://phab.mercurial-scm.org/D8385

hgext/hgk.py

@@ -358,7 +358,7 b' def revtree(ui, args, repo, full=b"tree"'
 )
 def revlist(ui, repo, *revs, **opts):
     """print revisions"""
-    if opts[b'header']:
+    if opts['header']:
         full = b"commit"
     else:
         full = None