py3: use `x.hex()` instead of `pycompat.sysstr(node.hex(x))`

tests: assume that `raw` attribute is present on original socket file object It seems like the original socket file object is always an io.BufferedIO instance. If not, the code will fail and we should try harder to get the socket object (e.g. if the original socket file object is unbuffered, we can get the `_sock` attribute directly from it).

tests: constant-fold a `pycompat.ispy3` in testlib/badserverext.py

tests: remove Python 2 special cases in test-stdio.py

py3: remove dead code to make file descriptors non-inheritable On Python 3, file descriptors are already non-inheritable by default.

py3: remove hack that removed flush argument from print() calls on Python 2

py3: remove long() compatibility code

zeroconf: constant-fold a `pycompat.ispy3` I’ve checked that both bytes and str gets passed as the `name` parameter, so the rest of the condition is still required. Because there aren’t really any tests for the extensions, I didn’t want to refactor it to pass a single type.