WIP: github: Reduce the list of libcxx windows test configurations to build

Author: mstorsjo

.github/workflows/libcxx-build-and-test.yaml

@@ -239,10 +239,6 @@ jobs:
       matrix:
         include:
         - { config: clang-cl-dll, mingw: false }
-        - { config: clang-cl-static, mingw: false }
-        - { config: clang-cl-no-vcruntime, mingw: false }
-        - { config: clang-cl-debug, mingw: false }
-        - { config: clang-cl-static-crt, mingw: false }
         - { config: mingw-dll, mingw: true }
         - { config: mingw-static, mingw: true }
         - { config: mingw-dll-i686, mingw: true }