Remove ARGV.env

Replace with `Homebrew.args.env`.

Part of #5730.

Library/Homebrew/extend/ARGV.rb

@@ -15,10 +15,6 @@ module HomebrewArgvExtension
     value "cc"
   end
 
-  def env
-    value "env"
-  end
-
   private
 
   def options_only

Library/Homebrew/extend/ENV.rb

@@ -6,7 +6,7 @@ require "extend/ENV/std"
 require "extend/ENV/super"
 
 def superenv?
-  ARGV.env != "std" && Superenv.bin
+  Homebrew.args.env != "std" && Superenv.bin
 end
 
 module EnvActivation

Library/Homebrew/formula_installer.rb

@@ -731,8 +731,8 @@ class FormulaInstaller
     args << "--cc=#{ARGV.cc}" if ARGV.cc
     args << "--keep-tmp" if Homebrew.args.keep_tmp?
 
-    if ARGV.env
-      args << "--env=#{ARGV.env}"
+    if Homebrew.args.env.present?
+      args << "--env=#{Homebrew.args.env}"
     elsif formula.env.std? || formula.deps.select(&:build?).any? { |d| d.name == "scons" }
       args << "--env=std"
     end