Rollback to last working slang (#131)

* Fix the broken CI build of playground

* Remove slang-reflect-header library that is no longer used

* Roll back to a working Slang commit

Author: jkwak-work

.github/workflows/jekyll-gh-pages.yml

@@ -36,6 +36,12 @@ jobs:
           mkdir slang-repo
           pushd slang-repo
           git clone https://github.com/shader-slang/slang.git
+
+          # Temporary workaround for the broken playground
+          pushd slang
+          git checkout 2631811e33ed231d785a06c1fd6d4a7e303d22f2
+          popd
+
           popd
           echo "$(git -C slang-repo/slang rev-parse HEAD)" >> key.txt