I've found myself in a situation where the amount of possible Issue Link Types is overwhelming for basic users, and I would like to delete some of them in order to simplify the process.
Unfortunately this not as easy as it sounds, as I suspect many of the available Types origin in installed apps and simply removing them could cause related Apps to stop working. It seems like in order to safely remove these Types I would have to verify their origin, but there doesn't seem to be any such information in Administration > Issues > Issue Linking.
Any ideas how to find the origin of Issue Link Types or verify their dependencies? I did try to google them with little success, and due to a high number of installed Apps in our instance it's hard to pinpoint any single one as the culprit.
There is no reference to it Jira-wise. If an app has a dependency on an issue link, Jira does not know about it. It might not even be an app/client existing inside Jira, could be a remote application/client somewhere else using those links via REST, or issue search. Short answer is, there is no easy way to get a concrete list of dependencies.
The only way you could do (part of) this is to go to Admin -> manage apps, look at the list of user-installed apps, and read the documentation for each one you have active to find out what link types they actually need to be there in Jira.
You should do the same for external integrations too, but Jira can't tell you what they are, as they're not inside it.