Related Lists are meant to provide you an easy way to identify the existing relationships in your data, it is only logical that you should be able to deactivate those that you don't need.
Deactivate Related Lists
To get started, click on your profile picture and then on 'Settings' (1). On the left-hand side menu, click on the option called 'Related Lists' (2).
Then, select the corresponding tab (1), to view all the existing Related Lists. Once there, just select the desired element and click the 'Deactivate' button (2).
It will be necessary that you confirm this process before your Related list becomes inactive by clicking on the 'Deactivate' button in the confirmation dialog box.
To know if a Related list has been deactivated, check the 'Active' column. 'No' means that the column is currently not active. You can always revert this by selecting the Related list and clicking on the 'Activate' button.