Permit cleanup to remove outdated keg-only formulae

This check is not really relevant anymore; old-style, pre-opt installs
date from 2012 at the very latest, so it is very unlikely that any
packages remain which still link against these.

Refs Homebrew/homebrew#48139.

Library/Homebrew/formula.rb

@@ -1484,7 +1484,7 @@ class Formula
     eligible_for_cleanup = []
     if installed?
       eligible_kegs = installed_kegs.select { |k| pkg_version > k.version }
-      if eligible_kegs.any? && eligible_for_cleanup?
+      if eligible_kegs.any?
         eligible_kegs.each do |keg|
           if keg.linked?
             opoo "Skipping (old) #{keg} due to it being linked"
@@ -1492,8 +1492,6 @@ class Formula
             eligible_for_cleanup << keg
           end
         end
-      else
-        eligible_kegs.each { |keg| opoo "Skipping (old) keg-only: #{keg}" }
       end
     elsif installed_prefixes.any? && !pinned?
       # If the cellar only has one version installed, don't complain
@@ -1504,25 +1502,6 @@ class Formula
     eligible_for_cleanup
   end
 
-  # @private
-  def eligible_for_cleanup?
-    # It used to be the case that keg-only kegs could not be cleaned up, because
-    # older brews were built against the full path to the keg-only keg. Then we
-    # introduced the opt symlink, and built against that instead. So provided
-    # no brew exists that was built against an old-style keg-only keg, we can
-    # remove it.
-    if !keg_only? || ARGV.force?
-      true
-    elsif opt_prefix.directory?
-      # SHA records were added to INSTALL_RECEIPTS the same day as opt symlinks
-      Formula.installed.select do |f|
-        f.deps.any? do |d|
-          d.to_formula.full_name == full_name rescue d.name == name
-        end
-      end.all? { |f| f.installed_prefixes.all? { |keg| Tab.for_keg(keg).HEAD } }
-    end
-  end
-
   private
 
   def exec_cmd(cmd, args, out, logfn)