Remove deprecation notice from system "xcodebuild"

The new xcodebuild method calls system "xcodebuild" underneath, so this
notice would always be printed. Instead we will just rely on the audit
check.

Fixes Homebrew/homebrew#27092.

Library/Homebrew/formula.rb

@@ -565,7 +565,6 @@ class Formula
     ohai "#{cmd} #{pretty_args*' '}".strip
 
     if cmd.to_s.start_with? "xcodebuild"
-      opoo %{system "xcodebuild" is deprecated, use the xcodebuild method instead}
       removed_ENV_variables.update(ENV.remove_cc_etc)
     end