readall: stop using no longer needed 'nostdout'

Since switching from `system` to `Utils.popen_read` we no longer need to
suppress Ruby's output of `Syntax OK` to `$stdout`.

Library/Homebrew/cmd/readall.rb

@@ -17,7 +17,6 @@ module Homebrew
       end
 
       failed = false
-      nostdout do
       workers = (0...Hardware::CPU.cores).map do
         Thread.new do
           begin
@@ -29,8 +28,7 @@ module Homebrew
           end
         end
       end
-        workers.map(&:join)
+      workers.each(&:join)
-      end
       Homebrew.failed = failed
     end