token-2022: [L-04] Comment that TransferCheckedWithFee works for all mints

[joncinque]

Problem

According to the Certora audit:

A TransferCheckedWithFee succeeds even if the mint account is not extended with TransferFeeConfig if the instruction argument expected_fees is zero. This makes TransferChecked redundant since it can always be replaced by TransferCheckedWithFee.

Recommendation:
Either not allow TransferCheckedWithFee to succeed when fees are not enabled, or document that this is an expected and allowed behavior.

Solution

Comment that it is intended for TransferCheckedWithFee to work with any mint.