[Caching] Remove CASFS clang module implemenation

Remove the CASFS based clang module implemenation as it is not longer
used.

include/swift/Basic/CASOptions.h

@@ -37,9 +37,6 @@ public:
   /// CASOptions
   clang::CASOptions CASOpts;
 
-  /// CASFS Root.
-  std::vector<std::string> CASFSRootIDs;
-
   /// Clang Include Trees.
   std::string ClangIncludeTree;
 
@@ -62,9 +59,8 @@ public:
   /// Check to see if a CASFileSystem is required.
   bool requireCASFS() const {
     return EnableCaching &&
-           (!CASFSRootIDs.empty() || !ClangIncludeTree.empty() ||
-            !ClangIncludeTreeFileList.empty() || !InputFileKey.empty() ||
-            !BridgingHeaderPCHCacheKey.empty());
+           (!ClangIncludeTree.empty() || !ClangIncludeTreeFileList.empty() ||
+            !InputFileKey.empty() || !BridgingHeaderPCHCacheKey.empty());
   }
 
   /// Return a hash code of any components from these options that should

include/swift/Basic/LangOptions.h

@@ -1094,12 +1094,6 @@ namespace swift {
     /// built and provided to the compiler invocation.
     bool DisableImplicitClangModules = false;
 
-    /// Enable ClangIncludeTree for explicit module builds scanning.
-    bool UseClangIncludeTree = false;
-
-    /// Using ClangIncludeTreeRoot for compilation.
-    bool HasClangIncludeTreeRoot = false;
-
     /// Whether the dependency scanner should construct all swift-frontend
     /// invocations directly from clang cc1 args.
     bool ClangImporterDirectCC1Scan = false;