Move release checklist to the wiki

release-checklist.md

-# For major release
-
-- Add new SPDX License list data
-
-# For release for new GHC version:
-
-- Update GHC flags in `normaliseGhcArgs`, and add the GHC version to
-  `supportedGHCVersions` (`Distribution.Simple.Program.GHC`)
-- Update `Language.Haskell.Extension` list, if there are new GHC extensions
-- Update `setupMinCabalVersionConstraint` (in `Distribution.Client.ProjectPlanning`)
-- Update `Cabal.Distribution.Simple.GHC` to include new GHC version
+the new release checklist is at https://github.com/haskell/cabal/wiki/Making-a-release (easier to edit)