Remove test case for ROS 1 and colcon

It generally works but it's not an officially supported configuration so we don't want to block CI for those cases. 

Especially here it's failing on a system package deprecation.

```
 #22 16.62 E: Package 'python3-pytest-rerunfailures' has no installation candidate
  #22 ERROR: process "/bin/sh -c for i in 1 2 3; do apt-get update && apt-get install -q -y python3-pytest-rerunfailures && apt-get clean && break || if [ $i -lt 3 ]; then sleep 5; else false; fi; done" did not complete successfully: exit code: 1
```

.github/workflows/ci.yaml

@@ -52,33 +52,6 @@ jobs:
       - name: Validate configration
         run: validate_config_index.py https://raw.githubusercontent.com/ros-infrastructure/ros_buildfarm_config/production/index.yaml
 
-  ros1_devel:
-    name: ROS 1 Devel
-    runs-on: ubuntu-20.04
-    strategy:
-      matrix:
-        python: ['3.5', '3.6']
-        build_tool: [null]
-        include:
-          - python: '3.6'
-            build_tool: colcon
-    steps:
-      - name: Check out project
-        uses: actions/checkout@v2
-      - name: Set up Python
-        uses: actions/setup-python@v2
-        with:
-          python-version: ${{matrix.python}}
-      - name: Install dependencies
-        uses: ./.github/actions/setup
-      - name: Run job
-        uses: ./.github/actions/devel
-        with:
-          ros_distro: noetic
-          os_code_name: focal
-          build_tool: ${{matrix.build_tool}}
-          repo: roscpp_core
-
   ros1_doc:
     name: ROS 1 Doc
     runs-on: ubuntu-20.04