remove reference agent from docker-compose (#1098)

<!-- The PR description should answer 2 important questions: -->

### What

We do not use the reference agent anymore, for local dev or for tests.

This confuses users who are using the open source repo and trying to
start engine. It also has a port conflict with the `custom_connector`
service. So this doesn't even work. Remove the reference agent.

### How

<!-- How is it trying to accomplish it (what are the implementation
steps)? -->

V3_GIT_ORIGIN_REV_ID: bf42f0c2c23b20bb86ac736e3bf560fa53fc32f3

v3/docker-compose.yaml

@@ -14,8 +14,6 @@ services:
       # Binding to localhost:3001 avoids conflict with dev_setup
       - 3001:3000
     depends_on:
-      reference_agent:
-        condition: service_started
       jaeger:
         condition: service_started
       auth_hook:
@@ -61,11 +59,6 @@ services:
       timeout: 1s
       retries: 5
 
-  reference_agent:
-    build: https://github.com/hasura/ndc-spec.git#v0.1.3
-    ports:
-      - 8102:8100
-
   auth_hook:
     build:
       dockerfile: dev-auth-webhook.Dockerfile