Revert "stream_wrap: reference handle before uv_write2"

It's segfaulting in release mode and asserting in debug mode:

  #
  # Fatal error in ../../deps/v8/src/api.h, line 297
  # CHECK(allow_empty_handle || that != __null) failed
  #

This reverts commit 99f0b022d528cc350f87150b5ecdf5c903aaeeb1.