Always add Plural metadata to dummy translations.

When this was conditional, we'd have plural info in some files, not in
others. Then we'd merge them, and msgcat would add wacky markers to
indicate the difference, and the metadata wouldn't parse.

i18n/make_dummy.py

@@ -42,11 +42,9 @@ def main(file, locale):
     for msg in pofile:
         converter.convert_msg(msg)
 
-    # If any message has a plural, then the file needs plural information.
     # Apply declaration for English pluralization rules so that ngettext will
     # do something reasonable.
-    if any(m.msgid_plural for m in pofile):
-        pofile.metadata['Plural-Forms'] = 'nplurals=2; plural=(n != 1);'
+    pofile.metadata['Plural-Forms'] = 'nplurals=2; plural=(n != 1);'
 
     new_file = new_filename(file, locale)
     create_dir_if_necessary(new_file)