Remove MinGW CI job

Removed for the same reason it was removed from SFML. GitHub Actions
switched to a version that expects different C runtime libraries
resulting in linker errors. Let's just remove this job since fixing
it is overkill for a project as simple as this.

.github/workflows/ci.yml

@@ -13,7 +13,6 @@ jobs:
         platform:
         - { name: Windows VS2019, os: windows-2019  }
         - { name: Windows VS2022, os: windows-2022  }
-        - { name: Windows MinGW,  os: windows-2022, flags: -GNinja -DCMAKE_C_COMPILER=gcc -DCMAKE_CXX_COMPILER=g++ }
         - { name: Linux GCC,      os: ubuntu-latest }
         - { name: Linux Clang,    os: ubuntu-latest, flags: -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ }
         - { name: macOS,          os: macos-latest  }
@@ -22,10 +21,6 @@ jobs:
         - { name: Static, flags: -DBUILD_SHARED_LIBS=FALSE }
 
     steps:
-    - name: Install Window Dependencies
-      if: runner.os == 'Windows'
-      run: choco install ninja
-
     - name: Install Linux Dependencies
       if: runner.os == 'Linux'
       run: sudo apt-get update && sudo apt-get install libxrandr-dev libxcursor-dev libudev-dev libopenal-dev libflac-dev libvorbis-dev libgl1-mesa-dev libegl1-mesa-dev