docs: remove commit hook stuff from contributing doc (#13608)

This change removes outdated information on commit hooks from the
contributing document. It also adds a clear pointer to the local dev env
setup documentation.

## Checklist
- [x] PR author has checked that all the criteria below are met
- The PR description includes an overview of the change
- The PR description articulates the motivation for the change
- The change includes tests OR the PR description describes a testing
strategy
- The PR description notes risks associated with the change, if any
- Newly-added code is easy to change
- The change follows the [library release note
guidelines](https://ddtrace.readthedocs.io/en/stable/releasenotes.html)
- The change includes or references documentation updates if necessary
- Backport labels are set (if
[applicable](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting))

## Reviewer Checklist
- [ ] Reviewer has checked that all the criteria below are met 
- Title is accurate
- All changes are related to the pull request's stated goal
- Avoids breaking
[API](https://ddtrace.readthedocs.io/en/stable/versioning.html#interfaces)
changes
- Testing strategy adequately addresses listed risks
- Newly-added code is easy to change
- Release note makes sense to a user of the library
- If necessary, author has acknowledged and discussed the performance
implications of this PR as reported in the benchmarks PR comment
- Backport labels are set in a manner that is consistent with the
[release branch maintenance
policy](https://ddtrace.readthedocs.io/en/latest/contributing.html#backporting)

Author: emmettbutler

docs/contributing.rst

@@ -12,6 +12,8 @@ if you'd like to report a bug or request a new feature.
 
 Before working on the library, install `docker <https://www.docker.com/products/docker>`_.
 
+If you're trying to set up a local development environment, read `this <https://github.com/DataDog/dd-trace-py/tree/main/docs/contributing-testing.rst>`_.
+
 Thanks for working with us!
 
 .. _change_process:
@@ -34,8 +36,6 @@ Correctness and code style are automatically checked in continuous integration,
 various tools including Flake8, Black, and MyPy. This means that code reviews don't need to worry about style
 and can focus on substance.
 
-If you get errors from ``git commit`` that mention "pre-commit", run ``$ rm .git/hooks/pre-commit`` and try again.
-
 Branches and Pull Requests
 --------------------------
 
@@ -69,17 +69,6 @@ Each minor version has its own branch.
 If your pull request is a ``fix`` or ``ci`` change, apply the backport labels corresponding to the minor
 versions that need the change.
 
-Commit Hooks
-------------
-
-The tracer library uses formatting/linting tools including black, flake8, and mypy.
-While these are run in each CI pipeline for pull requests, they are automated to run
-when you call `git commit` as pre-commit hooks to catch any formatting errors before
-you commit.
-
-To initialize the pre-commit hook script to run in your development
-branch, run ``$ hooks/autohook.sh install``.
-
 Implementation Guidelines
 =========================