Remove cross-db dbt_utils references

[clausherther]

This PR removes internal references to deprecated dbt_utils macros in favor of their dbt-core counterparts.

Closes #656

This is a:

• documentation update
• bug fix with no breaking changes
• new functionality
• a breaking change

All pull requests from community contributors should target the main branch (default).

Description & motivation

Several dbt-utils macros internally reference deprecated macros using the dbt_utils namespace. This triggers warnings in downstream models and packages.

Checklist

• This code is associated with an Issue which has been triaged and accepted for development.
• I have verified that these changes work locally on the following warehouses (Note: it's okay if you do not have access to all warehouses, this helps us understand what has been covered)
  • BigQuery
  • Postgres
  • Redshift
  • Snowflake
• I followed guidelines to ensure that my changes will work on "non-core" adapters by:
  • dispatching any new macro(s) so non-core adapters can also use them (e.g. the star() source)
  • using the limit_zero() macro in place of the literal string: limit 0
  • using dbt.type_* macros instead of explicit datatypes (e.g. dbt.type_timestamp() instead of TIMESTAMP
• I have updated the README.md (if applicable)
• I have added tests & descriptions to my models (and macros if applicable)
• I have added an entry to CHANGELOG.md

[joellabes]

This is spectacular @clausherther! Thanks for turning it around so quickly.

I have made a couple of tweaks to the README - let me know what you think. Mostly trying to reduce confusion for people who are still using 0.8.x or below but are probably going to be looking at this documentation.

[joellabes]

Thanks heaps @clausherther!