(actions) drop python3 support

Author: MatthijsBurgh

.github/workflows/main.yml

@@ -13,13 +13,10 @@ jobs:
           # Use a build matrix to test many builds in parallel
           # envvar defaults:
           #   WITH_CMAKE: false
-          #   WITH_PYTHON3: false
           #   WITH_IO: true
           #   WITH_CUDA: false
           #   WITH_CUDNN: false
           - BUILD_NAME: default-make
-          #   - BUILD_NAME: python3-make
-          #     WITH_PYTHON3: true
           - BUILD_NAME: no-io-make
             WITH_IO: false
           - BUILD_NAME: cuda-make
@@ -29,9 +26,6 @@ jobs:
             WITH_CUDNN: true
           - BUILD_NAME: default-cmake
             WITH_CMAKE: true
-          - BUILD_NAME: python3-cmake
-            WITH_CMAKE: true
-            WITH_PYTHON3: true
           - BUILD_NAME: no-io-cmake
             WITH_CMAKE: true
             WITH_IO: false