Revert "Reapply "[NFC] Explicitly pass a VFS when creating DiagnosticsEngine (llvm#115852)""

This reverts commit 5131c23.

Author: egorzhdan

lldb/source/Commands/CommandObjectTarget.cpp

@@ -2200,7 +2200,7 @@ class CommandObjectTargetModulesDumpClangPCMInfo : public CommandObjectParsed {
     }
 
     clang::CompilerInstance compiler;
-    compiler.createDiagnostics(*FileSystem::Instance().GetVirtualFileSystem());
+    compiler.createDiagnostics(*llvm::vfs::getRealFileSystem());
 
     const char *clang_args[] = {"clang", pcm_path};
     compiler.setInvocation(clang::createInvocation(clang_args));

lldb/source/Plugins/ExpressionParser/Clang/ClangModulesDeclVendor.cpp

@@ -706,9 +706,8 @@ ClangModulesDeclVendor::Create(Target &target) {
   auto diag_options_up =
       clang::CreateAndPopulateDiagOpts(compiler_invocation_argument_cstrs);
   llvm::IntrusiveRefCntPtr<clang::DiagnosticsEngine> diagnostics_engine =
-      clang::CompilerInstance::createDiagnostics(
-          *FileSystem::Instance().GetVirtualFileSystem(),
-          diag_options_up.release(), new StoringDiagnosticConsumer);
+      clang::CompilerInstance::createDiagnostics(diag_options_up.release(),
+                                                 new StoringDiagnosticConsumer);
 
   Log *log = GetLog(LLDBLog::Expressions);
   LLDB_LOG(log, "ClangModulesDeclVendor's compiler flags {0:$[ ]}",