Whatever those links are pointing to… is it going to be migrated to Discourse? For example, if those links point to blog posts, that you are turning into topics, then you could create permalinks: Redirect old forum URLs to new Discourse URLs
You could also remap those URLs to something else. Assuming the URLs have some common formatting, you could use REGEX and the remap command to replace them:
remap [--global,--regex] FROM TO
An example on how to use the command:
discourse remap --regex "\[\/?color(=[^\]]*)*]" "" # removing "color" bbcodesc