Remove deprecation warnings for tests to data_tests configs

[gshank]

Description

We are not going to actually deprecate the use of the "tests:" config. Although we prefer "data_tests:" because it's more precise and less confusing, and contrasts more logically with our newer "unit_tests:" definitions, the use of "tests:" will continue to work, so we should remove the actual deprecation warning.

Instead we will move this to the project auditing feature: dbt-labs/dbt-project-evaluator#489

Acceptance Criteria

No more warnings are issued and people who have set up a "warn_error_options" config for TestsConfigDeprecation do not get errors.

[jschintz-nytimes]

At least make an easy way to identify tests vs data_tests

I'd love to be able to run something like
dbt ls --resource-type test --exclude-resource-type data_test