chore(tests): remove agent v5 testing support (#4537)

The minimum supported Datadog Agent version of ddtrace is 7.28[^0] as of
ddtrace v1.0 which means we can drop testing support for it.

With this, support for the v0.3 traces endpoint could also be dropped
but maintaining it is little burden due to its overlap with v0.4.

[^0]: https://ddtrace.readthedocs.io/en/v1.0.0/versioning.html#release-support

Co-authored-by: Brett Langdon <brett.langdon@datadoghq.com>

.circleci/config.yml

@@ -509,19 +509,6 @@ jobs:
           store_coverage: false
           pattern: '^py.\+-profile'
 
-  integration_agent5:
-    <<: *machine_executor
-    steps:
-      - attach_workspace:
-          at: .
-      - checkout
-      - start_docker_services:
-          services: ddagent5
-      - run:
-          command: |
-            mv .riot .ddriot
-            ./scripts/ddtest riot -v run --pass-env -s 'integration-v5'
-
   integration_agent:
     <<: *machine_executor
     steps:
@@ -1162,7 +1149,6 @@ requires_tests: &requires_tests
     - grpc
     - httplib
     - httpx
-    - integration_agent5
     - integration_agent
     - integration_testagent
     - vendor
@@ -1261,7 +1247,6 @@ workflows:
       - grpc: *requires_base_venvs
       - httplib: *requires_base_venvs
       - httpx: *requires_base_venvs
-      - integration_agent5: *requires_base_venvs
       - integration_agent: *requires_base_venvs
       - integration_testagent: *requires_base_venvs
       - internal: *requires_base_venvs

releasenotes/notes/old-agent-8193550a76b21357.yaml

@@ -0,0 +1,7 @@
+---
+upgrade:
+  - |
+    tracer: support for Datadog Agent v5 has been dropped. Datadog Agent v5 is
+    no longer supported since ddtrace==1.0.0. See
+    https://ddtrace.readthedocs.io/en/v1.0.0/versioning.html#release-support
+    for the version support.

riotfile.py

@@ -292,12 +292,6 @@ def select_pys(min_version=MIN_PYTHON_VERSION, max_version=MAX_PYTHON_VERSION):
             command="pytest --no-cov {cmdargs} tests/integration/",
             pkgs={"msgpack": [latest]},
             venvs=[
-                Venv(
-                    name="integration-v5",
-                    env={
-                        "AGENT_VERSION": "v5",
-                    },
-                ),
                 Venv(
                     name="integration-latest",
                     env={