Don’t double‐newline specials in perdec

Don’t double‐newline specials in perdec

It’s not necessary to insert newlines (as pipes) before and after the
`sed` substitutions for pipe and backslash, because these substitutions
take place before the substitution for percent‐encoded characters
(which adds its own newlines). (The extra newlines are harmless, they
just mean `awk` gets a few more empty records to process.)