Remove extra #set_pipe_info method

* We can just set the instance variable directly.
* Pipes are already #sync = true when created.

Author: eregon

src/main/ruby/core/io.rb

@@ -871,7 +871,7 @@ def self.popen(*args)
 
     if readable and writable
       pipe = pa_read
-      pipe.set_pipe_info(pa_write)
+      pipe.instance_variable_set(:@write, pa_write)
     elsif readable
       pipe = pa_read
     elsif writable
@@ -2652,11 +2652,6 @@ def encode_with coder
 
 class IO::BidirectionalPipe < IO
 
-  def set_pipe_info(write)
-    @write = write
-    @sync = true
-  end
-
   ##
   # Closes ios and flushes any pending writes to the
   # operating system. The stream is unavailable for