gnu: ghc-mtl: Remove built-in Haskell package.

* gnu/packages/agda.scm (agda)[inputs]: Remove ghc-mtl.
* gnu/packages/games.scm (raincat)[inputs]: Remove ghc-mtl.
* gnu/packages/haskell-check.scm (ghc-tasty-ant-xml, ghc-tasty-golden,
ghc-tasty, ghc-tasty-kat, ghc-tasty-rerun,
ghc-crypto-cipher-tests)[inputs]: Remove ghc-mtl.
* gnu/packages/haskell-crypto.scm (ghc-asn1-encoding, ghc-pem, ghc-x509,
ghc-x509-store, ghc-x509-validation, ghc-x509-system)[inputs]: Remove
ghc-mtl.
* gnu/packages/haskell-web.scm (ghc-http, ghc-http-conduit,
ghc-yesod-core)[inputs]: Remove ghc-mtl.
* gnu/packages/haskell.scm (ghc-convertible, ghc-libxml, ghc-cgi,
ghc-happy, ghc-haskell-src-exts, ghc-resourcet, cabal-install,
ghc-indents, ghc-regex-base, ghc-regex-tdfa-rc, ghc-trifecta,
ghc-zip-archive, ghc-logict, ghc-exceptions, ghc-smallcheck, ghc-syb,
ghc-fgl, ghc-chasingbottoms, ghc-parsec, ghc-megaparsec, ghc-edisonapi,
ghc-edisoncore, ghc-mmorph, ghc-ifelse, ghc-kan-extensions, ghc-lens,
ghc-cheapskate, ghc-free, ghc-adjunctions, ghc-equivalence, ghc-texmath,
ghc-texmath-for-pandoc-1, ghc-highlighting-kate, ghc-th-reify-many,
ghc-th-orphans, ghc-geniplate-mirror, ghc-conduit, ghc-filemanip,
ghc-juicypixels, ghc-hslua, ghc-hourglass, ghc-skylighting,
ghc-skylighting-for-pandoc-1, ghc-pandoc, ghc-pandoc-1,
ghc-pandoc-citeproc, ghc-regex-tdfa, ghc-stmonadtrans, ghc-constraints,
ghc-lifted-async, ghc-shelly, ghc-hslogger, ghc-json, shellcheck,
ghc-vector-algorithms, ghc-monad-par-extras, ghc-monad-par,
ghc-monadrandom, ghc-either, ghc-rebase, ghc-aws, ghc-monad-logger,
ghc-persistent, ghc-bytes, ghc-missingh, ghc-operational,
ghc-chart)[inputs]: Remove ghc-mtl.
(ghc-conduit-combinators)[native-inputs]: Remove ghc-mtl.
(ghc-mtl): Remove variable.
* gnu/packages/idris.scm (idris)[inputs]: Remove ghc-mtl.
* gnu/packages/tls.scm (ghc-tls)[inputs]: Remove ghc-mtl.
* gnu/packages/version-control.scm (darcs, git-annex)[inputs]: Remove
ghc-mtl.
* gnu/packages/wm.scm (xmonad, ghc-xmonad-contrib)[inputs]: Remove
ghc-mtl.
* gnu/packages/xml.scm (ghc-hxt)[inputs]: Remove ghc-mtl.

gnu/packages/xml.scm

@@ -2078,7 +2078,6 @@ derivations of regular expressions.")
     (build-system haskell-build-system)
     (inputs
      `(("ghc-parsec" ,ghc-parsec)
-       ("ghc-mtl" ,ghc-mtl)
        ("ghc-hxt-charproperties" ,ghc-hxt-charproperties)
        ("ghc-hxt-unicode" ,ghc-hxt-unicode)
        ("ghc-hxt-regex-xmlschema" ,ghc-hxt-regex-xmlschema)