Remove Outdated Default Checks

[mitchelsellers]

Description of problem

DNN Platform in the past has provided a method to check for "default credentials" due to prior limitations in the platform about automatically creating users without forcing a password change.

DNN Platform has forced password changes for a number of years and these checks add complexity to the code and do not provide valuable long-term benefits and should be removed.

Description of solution

To follow the proper process the API check should be marked obsolete and the rest of the code removed.

Description of alternatives considered

We could leave this, but it adds extra work on every page load etc.