Remove experimental parser tests

[mikealfare]

Problem

These tests are not relevant to dbt-postgres. They test dbt-core functionality.

Solution

• Remove experimental parser tests from dbt-postgres
• Leave experimental parser tests in dbt-core
• Migrate get catalog unit tests from dbt-postgres to dbt-adapters

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX