I haven’t found way to stop it installing, but at least you can make it automatically removed afterwards. Just create /etc/updater/hook_postupdate/03_remove_wshaper.sh:
#!/bin/sh
opkg remove "luci-i18n-wshaper-cs"
opkg remove "luci-i18n-wshaper-en"
opkg remove "luci-app-wshaper"
opkg remove "wshaper"