Why do I have this? Am I being charged for this feature?
It sounds like a contractual holdover from way back in the days when the locally granted franchise agreement was allowed to require specific channels available to all subscribers. Some of those casrried a flat fee, others might have allowed for price escalation. If there is a charge for that programming today, it should be itemized on your monthly bill.
Last year some Viacom channels were removed from the TV Select package and moved to Digital Tier 2. Your services were there before that change. This Legacy Viacom Channel is a code that kept those channels for you to view, as newer customers had to get Digital Tier 2 for those channels. This was all rectified with a new carriage agreement that was signed and went into effect this past January. You can see old statements about the movement of MTV, BET, TV Land, and other Viacom channels. But the short answer is that you don't pay any extra for that channel code to be on your account.