Excuse for my English.
I have a licence serial code.
I have created 4 accounts because the statistics left and weapons/unlocks/perks not saving.
If there is a limit of accounts exists.
How to remove superfluous/unnecessary accounts?

I can't answer your first question, but I can tell you how to remove accounts. Log into the unwanted account, and click "Edit profile" on the top right. At the next page, click "Account settings" on the left. You should see an option to "Delete account". Just click on it and you're done.