Remove test timings

[rcomer]

🚀 Pull Request

Description

Here is some more Iris functionality that I did not know existed, until @pp-mo mentioned it the other day. Described by the removed comment

iris/lib/iris/tests/__init__.py

Lines 940 to 946 in 6eb0401

	# An environment variable controls whether test timings are output.
	#
	# NOTE: to run tests with timing output, nosetests cannot be used.
	# At present, that includes not using "python setup.py test"
	# The typically best way is like this :
	# $ export IRIS_TEST_TIMINGS=1
	# $ python -m unittest discover -s iris.tests

I tried to run this with unittest discover as the comment recommends, but got errors, particularly from test_pandas.py. I found that this functionality can be used with pytest -s -v, so if we do want to keep the functionality we should probably document that. I'm unsure if it can be made to work with pytest-xdist.

In any case, pytest provides its own functionality to tell you the timings of the slowest running tests via the --durations flag, and of course we now have some pytest tests which don't inherit from IrisTest, so won't work with the bespoke functionality unless we go through and add the decorator.

More generally, the more we can simplify these test classes, the better chance we have of eventually ditching unittest altogether.

This functionality was added at #2372.

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[lbdreyer]

Looking great! Thanks for doing this @rcomer !

I spotted one other mention of IrisTest_nometa here: https://github.com/SciTools/iris/blame/main/lib/iris/tests/graphics/README.md#L27

Do you mind also updating that in this PR?

[rcomer]

Thanks @lbdreyer, good spot! I only grepped the python files. Now fixed and also rebased to address the whatsnew conflict. I don't know why the CI isn't running 😕 [close and reopen fixed that]