Correct the initialization requirements for deflateInit2().

zlib.h

@@ -543,8 +543,7 @@ ZEXTERN int ZEXPORT deflateInit2 OF((z_streamp strm,
                                      int  strategy));
      This is another version of deflateInit with more compression options.  The
-   fields next_in, zalloc, zfree and opaque must be initialized before by the
-   caller.
+   fields zalloc, zfree and opaque must be initialized before by the caller.
      The method parameter is the compression method.  It must be Z_DEFLATED in
    this version of the library.