fix obviously wrong attoparsec parser

fix obviously wrong attoparsec parser

takeByteString can only be used at the end of a parser, not before other
input. This was a dumb enough mistake that I audited the rest of the
code base for similar mistakes. Pity that attoparsec cannot avoid it at
the type level.

Fixes git-annex forget propagation between repositories. (reversion
introduced in version 7.20190122)

Sponsored-by: Brock Spratlen on Patreon