Remove platform from compose file

I believe that the workaround introduced in PR #3562 is no longer
needed. Using a fresh project created with cookiecutter-django, I was
able to run the app with docker compose using the arm64 platform for the
django and postgres images, without any database connection issue.

I compared the version of libpq on the arm64 image with the one on the
amd64 image and they were identical.

If the workaround is no longer needed, it is preferable to use arm64 on
an M1 mac for better performance.

If any core contributers are using an M1 mac, it would be good to test
this before merging to ensure that this isn't just a quirk of my
machine.

If it helps, I'm using Docker Desktop v4.14.1 with Engine v20.10.21 and
compose v1.29.2, on macOS 12.6.

{{cookiecutter.project_slug}}/local.yml

@@ -11,7 +11,6 @@ services:
       dockerfile: ./compose/local/django/Dockerfile
     image: {{ cookiecutter.project_slug }}_local_django
     container_name: {{ cookiecutter.project_slug }}_local_django
-    platform: linux/x86_64
     depends_on:
       - postgres
       {%- if cookiecutter.use_celery == 'y' %}
@@ -44,7 +43,6 @@ services:
   docs:
     image: {{ cookiecutter.project_slug }}_local_docs
     container_name: {{ cookiecutter.project_slug }}_local_docs
-    platform: linux/x86_64
     build:
       context: .
       dockerfile: ./compose/local/docs/Dockerfile

{{cookiecutter.project_slug}}/production.yml

@@ -11,7 +11,6 @@ services:
       context: .
       dockerfile: ./compose/production/django/Dockerfile
     image: {{ cookiecutter.project_slug }}_production_django
-    platform: linux/x86_64
     depends_on:
       - postgres
       - redis