build(agd): use timestamps again; hashes weren't necessary

.github/actions/restore-node/action.yml

@@ -135,6 +135,8 @@ runs:
         if test -e ~/endo; then
           scripts/get-packed-versions.sh ~/endo | scripts/resolve-versions.sh
         fi
+        STAMPS=node_modules/.cache/agoric
+        mkdir -p "$STAMPS"
         yarn install
 
         if ! cmp -s <(git cat-file blob HEAD:package.json) package.json; then
@@ -147,34 +149,6 @@ runs:
           git checkout HEAD -- package.json
         fi
 
-        function diffsha1() {
-          stamp=$1
-          shift
-          find ${1+"$@"} -exec sha1sum {} \; | sort +1 > "$stamp.new" || true
-          if test ! -s "$stamp.new"; then
-            echo "No new dependencies found for $stamp" 1>&2
-            return 0
-          fi
-          diff -u "$stamp" "$stamp.new" || return 1
-          return 0
-        }
-
-        # Find the current list of package.jsons.
-        files=( package.json )
-        while IFS= read -r line; do
-          files+=( "$line" )
-        done < <(yarn -s workspaces info |
-          sed -ne '/"location":/{ s/.*": "//; s!",.*!/package.json!; p; }')
-
-        STAMPS=node_modules/.cache/agoric
-
-        mkdir -p "$STAMPS"
-        sum="$STAMPS/yarn-installed.sum"
-        diffsha1 "$sum" "${files[@]}" || {
-          mv "$sum.new" "$sum"
-        }
-        rm -f "$sum.new"
-
         if test -e ~/endo; then
           # Stage the redirected `yarn install` consequences.
           git add package.json yarn.lock