Remove ENV.expand_xcrun

This method is currently unused and after inspecting the git history, it
appears it may never have been used at all.

Library/Homebrew/extend/ENV/std.rb

@@ -138,16 +138,6 @@ module Stdenv
   end
   alias_method :gcc_4_0, :gcc_4_0_1
 
-  # if your formula doesn't like CC having spaces use this
-  def expand_xcrun
-    self['CC'] =~ %r{/usr/bin/xcrun (.*)}
-    self['CC'] = `/usr/bin/xcrun -find #{$1}`.chomp if $1
-    self['CXX'] =~ %r{/usr/bin/xcrun (.*)}
-    self['CXX'] = `/usr/bin/xcrun -find #{$1}`.chomp if $1
-    self['OBJC'] = self['CC']
-    self['OBJCXX'] = self['CXX']
-  end
-
   def gcc
     # Apple stopped shipping gcc-4.2 with Xcode 4.2
     # However they still provide a gcc symlink to llvm