Allow/relax upper bound on `packaging` dependency

[miketheman]

The current requirement on packaging is pinned:

python-bigquery/setup.py

Line 43 in e1aa921

"packaging >= 14.3, <22.0.0dev",

With the release of packaging 22.0, clients using the current release of this project cannot update and benefit from the released version (which removes the last dependency of pyparsing).

The upper boundary was pinned in #1263 - my suggestion would be to remove said upper boundary and release a new version of the library, so that clients have the flexibility to update packages with fewer conflicts.

[tswast]

@parthea @chalmerlowe @aribray Thoughts on this one? Seems like the packaging dependency matches our criteria in go/python-client-dependency-management#removing-some-upper-bounds, though perhaps we'd want to make sure we install a prerelease/nightly/git version of the package to catch issues early?

[parthea]

@tswast Could we drop packaging instead? We're no longer using it in other repositories

[tswast]

No, we cannot. We use it to compare versions of optional dependencies in this package.

[parthea]

If we want to keep the dependency on packaging then I think it's ok to remove the upper bound. I'd recommend trying to remove packaging as a dependency altogether since it's trivial to achieve the same behaviour with our own logic. In other words, we could write code to extract the versions with tests to confirm the behavior. WDYT?

[miketheman]

remove the upper bound.

100% agree with this as a "do this now", while the desire for

achieve the same behaviour with our own logic

can be done at one's leisure to remove the dependency altogether.