format: fix creating "RO copies" of dicts needlessly

...as we have a better construct for that now (since commit
'Solve a "read-only dict as API" question once forever').

Signed-off-by: Jan Pokorný <jpokorny@redhat.com>
format: cosmetics (max 80 chars per line)

Signed-off-by: Jan Pokorný <jpokorny@redhat.com>