make TemplateSchemaNoDetail tidier now that it doesn't have content

the schema was originally created so that it could not show content.
However, then it needed content conditionally for broadcast messages so
content was added back in.

Now that broadcasts no longer exist we can revert that - however, for a
template that has a specific list of expected keys, it's nicer to just
list those rather than maintain a huge list of exceptions that needs to
be modified every time a field changes on the template model

app/schemas.py

@@ -430,28 +430,14 @@ def validate_type(self, data, **kwargs):
 
 class TemplateSchemaNoDetail(TemplateSchema):
     class Meta(TemplateSchema.Meta):
-        exclude = TemplateSchema.Meta.exclude + (
-            "archived",
-            "created_at",
-            "created_by",
-            "created_by_id",
-            "hidden",
-            "letter_attachment",
-            "postage",
-            "process_type",
-            "redact_personalisation",
-            "reply_to",
-            "reply_to_text",
-            "service",
-            "service_letter_contact",
-            "subject",
-            "template_redacted",
-            "updated_at",
-            "version",
-            "letter_welsh_subject",
-            "letter_welsh_content",
-            "letter_languages",
-        )
+        fields = [
+            "folder",
+            "id",
+            "is_precompiled_letter",
+            "name",
+            "template_type",
+        ]
+        exclude = []
 
 
 class TemplateHistorySchema(BaseSchema):

tests/app/template/test_rest.py

@@ -612,45 +612,21 @@ def test_should_get_return_all_fields_by_default(
     }
 
 
-@pytest.mark.parametrize(
-    "extra_args",
-    (
-        {"detailed": False},
-        {"detailed": "False"},
-    ),
-)
-@pytest.mark.parametrize(
-    "template_type, expected_content",
-    (
-        (EMAIL_TYPE, None),
-        (SMS_TYPE, None),
-        (LETTER_TYPE, None),
-    ),
-)
-def test_should_not_return_content_and_subject_if_requested(
-    admin_request,
-    sample_service,
-    extra_args,
-    template_type,
-    expected_content,
-):
-    create_template(
-        sample_service,
-        template_type=template_type,
-        content="This is a test",
-    )
+@pytest.mark.parametrize("template_type", (EMAIL_TYPE, SMS_TYPE, LETTER_TYPE))
+def test_should_not_return_content_and_subject_if_requested(admin_request, sample_service, template_type):
+    create_template(sample_service, template_type=template_type)
     json_response = admin_request.get(
-        "template.get_all_templates_for_service", service_id=sample_service.id, **extra_args
+        "template.get_all_templates_for_service",
+        service_id=sample_service.id,
+        detailed=False,
     )
     assert json_response["data"][0].keys() == {
-        "content",
         "folder",
         "id",
         "is_precompiled_letter",
         "name",
         "template_type",
     }
-    assert json_response["data"][0]["content"] == expected_content
 
 
 @pytest.mark.parametrize(