remove warning filter in pytest plugin

[braingram]

Description

This PR removes the warnings filter in the asdf pytest plugin that was converting (most) warnings to errors:

asdf/pytest_asdf/plugin.py

Lines 242 to 245 in fcff366

	# Do not tolerate any warnings that occur during schema validation
	with warnings.catch_warnings():
	warnings.simplefilter("error")
	warnings.simplefilter("default", category=AsdfDeprecationWarning)

This filter is preventing all other warning filtering from having any effect. This is currently making it difficult to make the downstream weldx job pass as pandas is triggering a warning during several of the schema tests. Ideally we could ignore this warning (as it's a deprecation warning that weldx will need to address) by adding a filter to the weldx tox environment. However this is not possible because of the above warnings filter. Instead we would have to add the pandas warning to the pytest plugin warnings filter. With this PR we can add the warning filter to the tox.ini and it will have an effect.

As this PR removes the warnings filter internal to the asdf pytest plugin this does mean that any library that relied on this to turn warnings into errors during schema tests will need to add their own warnings filter (if they don't already have one).

Checklist:

• pre-commit checks ran successfully
• tests ran successfully
• for a public change, a changelog entry was added
• for a public change, documentation was updated
• for any new features, unit tests were added

[zacharyburnett]

LGTM, especially as it affects downstream

[braingram]

Thanks for the review!