audit: Remove FILEUTILS_METHODS constant

This constant hasn't been used since there was an `audit_line`
method, and as such is vestigial.

Library/Homebrew/dev-cmd/audit.rb

@@ -189,8 +189,6 @@ class FormulaAuditor
     swig
   ].freeze
 
-  FILEUTILS_METHODS = FileUtils.singleton_methods(false).map { |m| Regexp.escape(m) }.join "|"
-
   def initialize(formula, options = {})
     @formula = formula
     @new_formula = options[:new_formula]