Use original sources of goagain and manners

Replace forks of goagain and manners with updated versions in mainline. 

The patch from titanous/goagain has since been merged into rcrowley/goagain (https://github.com/rcrowley/goagain/commit/94f236e8b44e959172d86b32851179670087010e) and braintree/manners now uses ConnState in 1.3 for WaitGroup incrementing/decrementing, so https://github.com/cupcake/mannersagain/commit/2f14ecb136a20baf8cf6d508825416fe67486745 should no longer be needed.