It turns out the man(7) parser suffers from unintelligible handling

It turns out the man(7) parser suffers from unintelligible handling
of block rewinding, just like then mdoc(7) parser did.
First step in getting rid of rew_scope():
Replace the only call where the target block is known.
This commit is analogous to mdoc_macro.c rev. 1.167.
One down, three to go.