Ci #34131 rm slow fixtures
- [ x ] Part of #34131 
- [ x ] passes `black pandas`
- [ x ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ FAIL ] tests passed for 11 of 12 files changed. 6 tests fail inside the file `pandas/core/arrays/datetimes.py` , but there are not concerned by this PR. So I decide to push anyway.

I went through tests tagged with `@pytest.mark.slow` and take a look at the duration. The test is unmarked if the test duration is below 1 second.
note: I considered the total time for each combination in case of parameters

A total of 76 flags `slow` were unmark, so we can focus on "real" slow tests.


