Make Field.db_parameters() use db_type()

[blueyed]

This reverts parts of ca9c3cd, which appear to have been made unintentionally.

It removes support for db_type to return the "CHECK (%s)" constraint suffix.
Internal code appears to use db_parameters for this.

Fixes https://code.djangoproject.com/ticket/22260.

This needs tests. Please point me at where to put them, and how to test this best.

[ericpalakovichcarr]

This seems to work well. Could you make this PR against my (@BigSassy) public django repository, so I can then merge it into my pull request? I have the testing in place for migrations in Geodjango. With your code I think we'll have these tickets solved.

[blueyed]

@BigSassy
Great!
I think you can better cherry-pick it from my repo:

git remote add blueyed https://github.com/blueyed/django
git fetch blueyed
# (in your branch):
git cherry-pick f1b2e7d0b48c2be6177100c67e8d339ee02e2bf4

btw: when using hub, it would be just git cherry-pick https://github.com/blueyed/django/commit/f1b2e7d0b48c2be6177100c67e8d339ee02e2bf4.

If you still think, I should open a PR on your repo, then you should probably sync/update it first (it's 16 days behind).

[ericpalakovichcarr]

Got it, and thanks! I'm new to this stuff, so I appreciate you spelling out how to get your code into mine :)

[mjtamlyn]

Closing in favour of #2366