Interesting use case:
1. Script 1 with ScriptApp trigger management associated as an image link in a Google Site
2. Created a new instance of the script under a new account and update the image link
3. Deleted the container script 1 within the Google Site
4. A user visited the Google Site to invoke the script, but the page was cached pointing to the previous script 1.
5. The on-error trap emails are being emailed to me every time the "deleted" script runs.
How do I delete or stop these triggers?
In the Script Editor, You can also check for a project's triggers programmatically, then work with that trigger and it's source:
See https://developers.google.com/apps-script/reference/script/script-app for more
If you know the user that installed the trigger you could ask them to do to the "All my triggers" menu item in the script editor, find the trigger and delete it.
In the on-error email, there is a link to manage triggers. Make sure that the triggers are really gone. I had this issue with a set of shared spreadsheets, where I thought I had removed all the triggers, but my partner still had some enabled.