Remove redundant assignment in asyncio.streams.StreamReaderProtocol.connection_lost()

[maurycy]

Nothing fancy.

The variable is never used. The only other occurences of the string are completely not related:

% rg _stream_writer
Modules/_testcapi/codec.c
115:codec_stream_writer(PyObject *Py_UNUSED(module), PyObject *args)
200:    {"codec_stream_writer", codec_stream_writer, METH_VARARGS},

Lib/test/test_capi/test_codecs.py
734:    def test_codec_stream_writer(self):
735:        codec_stream_writer = _testcapi.codec_stream_writer
741:                    writer = codec_stream_writer(encoding, stream, errors)
745:                codec_stream_writer(NULL, stream, 'strict')
%

I don't think this requires a NEWS entry. It has no user-visible effects.

[python-cla-bot]

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[serhiy-storchaka]

LGTM. 👍

The _stream_writer attribute was removed in a355f60 (#114914).