Fix 75958: Remove true return when isn't helpful

[carusogabriel]

As described in #75958, some Spl* methods have an always return true, which isn't helpful if it can't have a return false somehow.

[krakjoe]

You can't do this, it breaks bc.

This hasn't been thought through :)

[nikic]

Obviously we can't change this in 7.1, but this might be appropriate for master, given how unlikely it is that anyone relies on this? Alternatively, it might be good to have a list somewhere of minor BC breaking changes like this that we should make in 8.0.

[carusogabriel]

@krakjoe Sorry forgot that changing function return type is a BC 😞

But, always return true functions isn't healthy for our code, right? bool, okay, but always true? 🤔

As @nikic, maybe something for master?