I currently have a slot for Steel Wing, but I want to change it. My other moves include Heat Wave, Solar Beam, and Fly.
If you want to get rid of your Charizard's Steel Wing from its moveset, I'd say go with Dragon Claw. This move can be boosted by Mega Charizard X's Tough Claws ability as well as grant it STAB in this form. Even if you use Mega Charizard Y instead, its 80 base power compared to Shadow Claw's 70 is worth it. Also, Y's Drought ability will allow you to use Solar Beam in one turn instead of having to absorb the sunlight on the first turn and then attack on the second turn. It has STAB Fly in this form. Both forms have STAB Heat Wave.