Would you like to delete the default material profiles in Cura? Look no further!
For some reason Ultimaker does not support the removal of default materials, but it can simple be done by remove the files xml files associated with each profile.
On Windows go to c:\Program Files\<your version of Cura)\resources\materials
Delete all the files, this will remove all default material profiles.
If you have already created custom profiles, don’t worry, that are kept else where. (eks: c:\Users\<username>\AppData\Roaming\cura\<version>\materials\)