Remove redundant check

* @sync was checked before this branch.

Author: eregon

src/main/ruby/truffleruby/core/io.rb

@@ -2465,7 +2465,7 @@ def write(data)
 
       while bytes_to_write > 0
         bytes_to_write -= @ibuffer.unshift(data, data.bytesize - bytes_to_write)
-        @ibuffer.empty_to self if @ibuffer.full? or sync
+        @ibuffer.empty_to self if @ibuffer.full?
       end
     end