fn: remove redundant Reduce function

This commit removes Reduce since we already have both Foldl and Foldr.

fn/func.go

@@ -1,17 +0,0 @@
-package fn
-
-// Reducer represents a function that takes an accumulator and the value, then
-// returns a new accumulator.
-type Reducer[T, V any] func(accum T, value V) T
-
-// Reduce takes a slice of something, and a reducer, and produces a final
-// accumulated value.
-func Reduce[T any, V any, S []V](s S, f Reducer[T, V]) T {
-	var accum T
-
-	for _, x := range s {
-		accum = f(accum, x)
-	}
-
-	return accum
-}