Move `iserv` into `utils` and change package name from `iserv-bin` to `iserv`

This is done for consistency. We usually call the package file the same name the
folder has.  The move into `utils` is done so that we can move the library into
`libraries/iserv` and the proxy into `utils/iserv-proxy` and then break the
`iserv.cabal` apart.  This will make building the cross compiler with TH
simpler, because we can build the library and proxy as separate packages.

Test Plan: ./validate

Reviewers: bgamari, goldfire, erikd

Reviewed By: bgamari

Subscribers: rwbarton, thomie, carter

Differential Revision: https://phabricator.haskell.org/D4436