Bug 1770791 - Remove duplicate initialization in python glean package

[arai-a]

for bug 1770791

On Windows, Creating FdLogger twice causes the subsequent subprocess operation somehow fail.
And apparently the duplicate initialization is completely unnecessary.
So, applied 2 fixes, both on Rust side and Python side.

Rust side's glean_enable_logging_to_fd uses OnceCell to prevent subsequent call overwriting the value,
but fd_logger::FdLogger::new(fd) is not guarded.
So, it should check FD_LOGGER.get().is_some() before fd_logger::FdLogger::new(fd).

Python side calls setup_logging twice, first time from _ffi.py top-level, and second time from glean.py top-level.
Either of them should be removed, and I've removed the former one.

The attached testcase fails on windows, with py.test -s tests/test_subprocess.py.
the -s option seems to be necessary to hit the problematic case.

[badboy]

Turns out our Python Windows tests have been broken for a while. Grmpf.
(See https://app.circleci.com/pipelines/github/mozilla/glean/9332/workflows/86672023-5c22-450d-b756-7904a2b3a1a5/jobs/173298 -- they crash, but don't report that as an error value).

Gonna go with your fix though, and fix CI in a followup.