The whole mechanic of Invoke works on the premise of calling the invocation of Galakrond. So to remove it would essentially destroy the whole mechanic itself.
A better option (if were required) would be to take a better look at the actual invocations themselves or the final version/s of Galakrond. For example, getting a free Arcanite Reaper has been discussed as being a little too overpowered. That, and look at the cards that trigger Invokes and adjust the balance. That Shaman card that Invokes twice, for example, should probably never have been a thing. Invokes are already super-powerful. So invoking twice for relatively little extra cost is definitely a problem.