How do you clear share actions bound to ‘copy to clipboard’?
There are multiple ways to clear "default actions":


Walking through the list of apps in Settings&rarr;Apps&rarr;Manage Apps, looking at each entry whether it has a "Clear defaults" button, and hit that (not very user-friendly -- and in this special case obviously not applyable, as the action seems not bound to a special app)
Using a helper app like e.g. Default App Manager or DefaultApp Reset (much more user-friendly -- but not suitable in this case, for the same reason as the previous point)
Installing another app which uses the same intent (in case of a "homescreen launcher" and the "home" key, another launcher, to give an example) -- not always easy to figure out what app might be fitting for this purpose. This is what lead to success in our case here, by installing Andmade Share
Note: You do not need to keep that app installed. It's the installation of the app which "drops" the default. This is also the purpose why the next item works:
Updating/uninstalling one of the apps currently using this intent (to take above example: that's why you will be asked again when your launcher received an update) -- this point just for completeness :)