refactor: remove unused core variables

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new (yet unpublished) tests lean heavily toward integration testing more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.

modules/editor/evil/init.el

@@ -19,7 +19,7 @@
 ;;    disable modules, and to reduce the effort required to maintain our copy of
 ;;    `evil-collection-list' (now I can just copy it from time to time).
 
-(when (and doom-interactive-p
+(when (and (not noninteractive)
            (not doom-reloading-p)
            (featurep! +everywhere))