test-driver.py: remove bufsize=1 from Popen calls

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

nixos/lib/test-driver/test-driver.py

@@ -110,7 +110,6 @@ def create_vlan(vlan_nr: str) -> Tuple[str, str, "subprocess.Popen[bytes]", Any]
     pty_master, pty_slave = pty.openpty()
     vde_process = subprocess.Popen(
         ["vde_switch", "-s", vde_socket, "--dirmode", "0700"],
-        bufsize=1,
         stdin=pty_slave,
         stdout=subprocess.PIPE,
         stderr=subprocess.PIPE,
@@ -748,7 +747,6 @@ class Machine:
 
         self.process = subprocess.Popen(
             self.script,
-            bufsize=1,
             stdin=subprocess.DEVNULL,
             stdout=subprocess.PIPE,
             stderr=subprocess.STDOUT,