Remove dead code for commandline parsing

Authored by monoidal on Aug 28 2018, 5:52 AM.

Description

Remove dead code for commandline parsing

Summary:
PrefixPred and AnySuffixPred are not used
since static flags were removed in bbd3c399939.

Test Plan: validate

Reviewers: bgamari, tdammers

Reviewed By: tdammers

Subscribers: rwbarton, carter

Differential Revision: https://phabricator.haskell.org/D5111