In response to a feature-request on Meta Stack Overflow: Allow retracting flags on deleted posts even if you can't view deleted posts, I created a userscript which allows you to retract flags directly from the "Flagged Posts for [User]" page in the user profile.
Click the following link: Install
As far as I know, there's no way to determine whether a flag is a post flag or a comment flag, so the script displays a "retract" button next to both types of flag; but as comment flags cannot be retracted, you get an error when trying to retract a comment flag.
Please report any bugs on the Issues page on the GitHub repository.
groupis a URL parameter with a value different than 4 (meaning, you're not filtering by comment flags).