Simplify down to one stack.yaml (#379)

As discussed on Matrix.

Since we don't use this for user installation, nor for testing multiple
versions of GHC (we have Haskell-CI based on `cabal` for that), the only
use of this is to provide a dev setup for stack users. As such, one
`stack.yaml` should be sufficient.

Author: michaelpj

stack-8.10.2.yaml

@@ -0,0 +1,11 @@
+resolver: lts-18.18 # GHC 8.10.7
+
+packages:
+- ./lsp
+- ./lsp-types
+- ./lsp-test
+
+flags: {}
+extra-package-dbs: []
+nix:
+  packages: [icu]