Use true as return types for SplHeap

[Girgias]

No description provided.

[kocsismate]

So we have given up trying to make these return types void? Or will we have a change to do so when we convert the tentative return types to real ones?

[Girgias]

So we have given up trying to make these return types void? Or will we have a change to do so when we convert the tentative return types to real ones?

Having true or void is basically the same, and considering the scope of it and how widespread true as a return type is IDK if this wouldn't even require an RFC :|