Clean up some sloppy coding in repl_gram.y.

Remove unused copy-and-pasted macro definitions, and improve formatting
of recently-added productions.

I got interested in this because buildfarm member protosciurus has been
crashing in "bison repl_gram.y" since commit 858ec118.  It's a long shot
that this will fix that, though maybe the missing trailing semicolon
has something to do with it?  In any case, there's no need to approve
of dead code, nor of code whose formatting isn't even self-consistent
let alone consistent with what's around it.