doom-debug-p and doom-interactive-p have always been intentionally
redundant, because changing the variables they replaced had other
side-effects, which made writing tests for them difficult. Since our
new (yet unpublished) tests lean heavily toward integration testing more
than unit testing, this becomes an implementation detail.
And doom-init-p's only use was refactor out at some point in the past,
so it's no longer used.
Also done to reduce Doom's footprint, in general.