Remove large buffer_size for self._buffer as it does not add performance

Author: rhpvorderman

src/isal/igzip.py

@@ -167,7 +167,7 @@ def __init__(self, filename=None, mode=None,
                                                   0)
         if self.mode == READ:
             raw = _IGzipReader(self.fileobj)
-            self._buffer = io.BufferedReader(raw, buffer_size=READ_BUFFER_SIZE)
+            self._buffer = io.BufferedReader(raw)
 
     def __repr__(self):
         s = repr(self.fileobj)