Revert "FormulaInstaller: flush before closing writes."

This reverts commit 5ce8f7a3a494e1d8e812369301fd4c4a05a7d9b7.

Library/Homebrew/build.rb

@@ -46,7 +46,6 @@ def main
 rescue Exception => e
   unless error_pipe.nil?
     e.continuation = nil if ARGV.debug?
-    error_pipe.flush
     Marshal.dump(e, error_pipe)
     error_pipe.close
     exit! 1

Library/Homebrew/formula_installer.rb

@@ -371,7 +371,6 @@ class FormulaInstaller
         read.close
         exec(*args)
       rescue Exception => e
-        write.flush
         Marshal.dump(e, write)
         write.close
         exit! 1
@@ -379,7 +378,6 @@ class FormulaInstaller
     end
 
     ignore_interrupts(:quietly) do # the fork will receive the interrupt and marshall it back
-      write.flush
       write.close
       Process.wait
       data = read.read