Is it possible to delete useless links on friendly portals?

Solution 1:

There is no way to destroy own faction link, field or resonator (yet).

You can let the resonators decay, this will only takes 9 days if nobody recharges or attacks the portal and it will destroy all existing links.

Solution 2:

It is now possible to delete friendly links.

With the introduction of the ADA Refactor and Jarvis Virus items, you can change faction ownership of a portal by using the appropriate object on any portal (provided you have enough XM): such action destroys all links and fields connected to it.

This works even for friendly portals, so, if you flip a portal from your faction to the opposing one, you can destroy its links (and then eventually re-capture the portal and recreate only the links you need).