The MLC (Mechanical Licensing Collective) Notified Me to Relinquish my Works to DistroKid. Should I Do That?

When you sign up for DistroKid Publishing, DistroKid becomes your publishing administrator. 

As your publishing admin, DistroKid will collect your mechanical royalties from the MLC on your behalf. In this case, "relinquishing" your works to DistroKid simply means that you are giving DistroKid permission to collect those royalties for you. You're not giving up any rights to your music when you do this.