According to Python documentation [0], `bufsize=1` is only meaningful in
text mode. As we don't pass in an argument called `universal_newlines`,
`encoding`, `errors` or `text` the file objects aren't opened in text
mode, which means the argument is ignored with a warning in Python 3.8.
line buffering (buffering=1) isn't supported in binary mode,
the default buffer size will be used
This commit removes this warning that appared when using
interactive test driver built with `-A driver`. This is done by
removing `bufsize=1` from Popen calls.
The default parameter when unspecified for `bufsize` is `-1` which
according to the documentation will be interpreted as
`io.DEFAULT_BUFFER_SIZE`. As mentioned by a warning, Python already
uses default buffer size when providing `buffering=1` parameter for
file objects not opened in text mode.
[0]: https://docs.python.org/3/library/subprocess.html#subprocess.Popen
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