templatespec: logcmdutil.templatespec() gets either template or mapfile

The callers of the function already never pass (non-`None`) values for
both, so let's check that and call the new factory functions.

Differential Revision: https://phab.mercurial-scm.org/D8846

mercurial/logcmdutil.py

@@ -603,12 +603,13 b' class changesettemplater(changesetprinte'
 
 
 def templatespec(tmpl, mapfile):
+    assert not (tmpl and mapfile)
+    if mapfile:
+        return formatter.mapfile_templatespec(b'changeset', mapfile)
+    else:
     if pycompat.ispy3:
         assert not isinstance(tmpl, str), b'tmpl must not be a str'
-    if mapfile:
-        return formatter.templatespec(b'changeset', tmpl, mapfile)
-    else:
-        return formatter.templatespec(b'', tmpl, None)
+        return formatter.literal_templatespec(tmpl)
 
 
 def _lookuptemplate(ui, tmpl, style):