py3: require values in changelog extras to be bytes

I don't know what happened here because b436059c1cca (py3: use
pycompat.bytestr() on extra values because it can be int, 2019-02-05)
came about b44a47214122 (py3: use string for "close" value in commit
extras, 2018-02-11). Whatever happened, we shouldn't need to convert
the values to bytes now. It's better to not convert because that might
cover up bugs where someone sets a unicode value in the extras and
that works until the unicode value happens to contain non-ascii (at
which point it will fail because `bytestr()` expects its argument to
be ascii if it's unicode).

Differential Revision: https://phab.mercurial-scm.org/D8332

mercurial/changelog.py

@@ -82,10 +82,7 b' def decodeextra(text):'
 
 def encodeextra(d):
     # keys must be sorted to produce a deterministic changelog entry
-    items = [
-        _string_escape(b'%s:%s' % (k, pycompat.bytestr(d[k])))
-        for k in sorted(d)
-    ]
+    items = [_string_escape(b'%s:%s' % (k, d[k])) for k in sorted(d)]
     return b"\0".join(items)