I want to not claim my 21 year old son for college residency reasons, do I simply remove him as a dependent?

Yes delete him from My Info.

If you wish to remove your college student dependent whom you already included on your return, follow these steps if using TurboTax Online:

1. Open or continue your return in TurboTax.
2. Select My Info in the menu.
3. Select the Add another dependent button if you need to add someone. Select the trash can icon next to the name of a dependent to remove them. We'll ask you to confirm before we take them off your return.

In the Desktop version, go to the Personal Info tab.

If your income is too high to claim the AOTC or LLTC and your student has enough taxable income of their own such that they would owe federal income tax, you can elect to forego claiming them as a dependent, allowing them to claim any credit to which they may be entitled on their own tax return. 

See this TurboTax tips article for more information.

@lwaddoups