Disable the systems reports in CRM

There are two ways, first through the solution, hide it by removing the display options:

Remove all the display in area

And do not to save and publish (for report I think it's optional, but can do it also)

Then, other way, you can change the Visibility by changing the Ownership type from organization to individual.

But, you cannot do it through solution, instead, go to the Sales -> Reports

Then click Edit, change the Viewable..

Once you change the viewable, only the individual owner can see this report, unless the owner share it out.

https://community.dynamics.com/crm/f/117/t/149132