Yeah there is always a shutoff in the cold water into the heater, and each faucet (both hot and cold) has a shut off, but no shut off to shower. I have never seen any water heater only has outlet / hot shutoff but no inlet shutoff.How does that work? Unless you somehow shut off the cold water going into the heater it will leak regardless of what you did to your faucets. Your plumbing out be configured differently than mine. Shutting off faucets under the sink has no impact on the cold water entering the heater.
If you want to take out the water heater you have to shut off the hot side of the faucet inlet, the water heater's cold water inlet, and absolutely do not use the shower. If you take cold shower then this may be a problem because some cold water will backflow into the hot side. If you don't shower when the water heater is out, you should not get any water coming out of the hot side.