[ci] Revert happy install workaround (#1174)

CI builds are failing with linker errors trying to install happy. This
workaround no longer appears to be needed.

Remove the manual install step.

appveyor.yml

@@ -117,10 +117,6 @@
 
             choco install haskell-stack -y
 
-            # temp workaround: install ghc for happy install
-
-            choco install ghc --version 8.0.1 -y
-
             choco install dotnetcore-sdk -y
 
             # choco install updated the path, so re-read them from the registry and reset $env:path
@@ -131,12 +127,6 @@
 
             $env:Path = "$machinePath;$userPath"
 
-            # temp workaround: run cabal update and install happy
-
-            cabal update
-
-            cabal install happy-1.19.5
-
             if ($env:BOND_BUILD -eq "Doc") {
 
                 choco install pandoc --version 1.19.2  -y