;ci: push: shouldn't need to restore timestamps with new stack

.github/workflows/push.yml

@@ -40,21 +40,6 @@ jobs:
 
     - name: Check out
       uses: actions/checkout@v2
-      # deep clone so we can restore timestamps (see below)
-      with:
-        fetch-depth: 0
-
-    # Restore timestamps to help stack not rebuild unchanged files.
-    # https://stackoverflow.com/questions/60906336
-    # https://stackoverflow.com/a/36243002/84401
-    # https://www.reddit.com/r/haskell/comments/g00ldn/haskell_stack_on_github_actions/
-    - name: Restore source file timestamps
-      run: |
-        git ls-tree -r --name-only HEAD | while read filename; do
-          TS="$(git log -1 --format="%ct" -- ${filename})"
-          touch "${filename}" -mt "$(date --date="@$TS" "+%Y%m%d%H%M.%S")"
-        done
-      # help emacs highlighter: "
 
     # things to be cached/restored: