Avoid building the parts we don't use that drag in extra dependencies.

Index: cabal.project
--- cabal.project.orig
+++ cabal.project
@@ -1,17 +1,5 @@
-with-compiler: ghc-8.8.4
-tests: True
-
 packages: cabal-bundler
-packages: cabal-deps
-packages: cabal-diff
-packages: cabal-docspec
-packages: cabal-env
-packages: cabal-hie
-packages: cabal-iface-query
 
-packages: cabal-store-check
-packages: cabal-store-gc
-
 packages: peura
 
 package cabal-bundler
@@ -36,5 +24,4 @@ constraints: directory     installed
 constraints: process       installed
 constraints: transformers  installed
 
-packages: https://oleg.fi/gentle-introduction-2021.2.tar.gz
--- packages: gentle-introduction-2021.1.tar.gz
+packages: ../gentle-introduction-2021.2
