py3: don't double-convert "opts" to bytes

The "opts" are already converted to bytes at the beginning of the
function. Doing it twice results in a crash, which makes
test-uncommit.t fail. The extra call was added recently, in
ff1ff2aae132 (uncommit: add support to modify the commit message and
date, 2019-09-07). test-uncommit.t passes again after this patch.

Differential Revision: https://phab.mercurial-scm.org/D6864

hgext/uncommit.py

@@ -177,7 +177,7 b' def uncommit(ui, repo, *pats, **opts):'
         with repo.transaction('uncommit'):
             if not (opts[b'message'] or opts[b'logfile']):
                 opts[b'message'] = old.description()
-            message = cmdutil.logmessage(ui, pycompat.byteskwargs(opts))
+            message = cmdutil.logmessage(ui, opts)
 
             keepcommit = pats
             if not keepcommit: