[FIX] account_cashbox: Remove obsolete unique constraint from account_cashbox_session due to new constraint

[rov-adhoc]

added in https://github.com/ingadhoc/account-payment/commit/db574bf536e815d10221859924381e4a3a86af4d#diff-fd2084468cbef678a2cb52e2257b09797d716c4ef6031d237b29f544ff6c0d77L40

[roboadhoc]

Pull request status dashboard.

[maq-adhoc]

@roboadhoc r+