Stop running "prune" as part of "cleanup"

Rationale: "prune" is slow, does not need to be run as often as
"cleanup", and is potentially destructive to things like empty
directories that Homebrew did not create. Thus we should let users run
`brew prune` only when they wish to, while still being able to use `brew
cleanup`.

Closes Homebrew/homebrew#19863.

Library/Homebrew/cmd/cleanup.rb

@@ -1,7 +1,6 @@
 require 'formula'
 require 'keg'
 require 'bottles'
-require 'cmd/prune'
 
 module Homebrew extend self
 
@@ -11,8 +10,6 @@ module Homebrew extend self
     if ARGV.named.empty?
       cleanup_cellar
       cleanup_cache
-      Homebrew.prune
-
       rm_DS_Store unless ARGV.dry_run?
     else
       ARGV.formulae.each { |f| cleanup_formula(f) }