Prune unneeded replace directives from staging go.mod files

Author: liggitt

hack/update-vendor.sh

@@ -240,6 +240,14 @@ for repo in $(tsort "${TMP_DIR}/tidy_deps.txt"); do
 $(go mod why ${loopback_deps})"
       exit 1
     fi
+
+    # prune unused pinned replace directives
+    comm -23 \
+      <(go mod edit -json | jq -r '.Replace[] | select(.Old.Path == .New.Path) | select(.New.Version != null) | .Old.Path' | sort) \
+      <(go list -m -json all | jq -r .Path | sort) |
+    xargs -L 1 -I {} echo "-dropreplace={}" |
+    xargs -L 100 go mod edit -fmt
+
   popd >/dev/null 2>&1
 done
 echo "=== tidying root" >> "${LOG_FILE}"