Change 'optional-packages' default on missing cabal.project

Fixes #6739

Author: hasufell

cabal-install/Distribution/Client/ProjectConfig.hs

@@ -544,8 +544,9 @@ readProjectLocalConfigOrDefault verbosity distDirLayout = do
         -- We expect a package in the current directory.
         projectPackages         = [ "./*.cabal" ],
 
-        -- This is to automatically pick up deps that we unpack locally.
-        projectPackagesOptional = [ "./*/*.cabal" ],
+        -- This was [ "./*/*.cabal" ] previously, but
+        -- confused users: https://github.com/haskell/cabal/issues/6739
+        projectPackagesOptional = [ ],
 
         projectConfigProvenance = Set.singleton Implicit
       }