[lldb][CPlusPlus][NFCI] Remove redundant construction of ClangASTImporter

[Michael137]

Summary

The usage of this variable was removed in 4f14c17df70916913d71914343dd4f6c709e218d.

This is no longer used inside this file. Since the call to
GetPersistentExpressionStateForLanguage has side-effects I marked this
NFCI. But there is no good reason we need this here.

lldb/source/Plugins/Language/CPlusPlus/BlockPointer.cpp

if (auto err = type_system_or_err.takeError()) {
       return;
     }
 
     auto ts = block_pointer_type.GetTypeSystem();
     auto clang_ast_context = ts.dyn_cast_or_null<TypeSystemClang>();
     if (!clang_ast_context)
       return;
 
-    std::shared_ptr<ClangASTImporter> clang_ast_importer;
-    auto *state = target_sp->GetPersistentExpressionStateForLanguage(
-        lldb::eLanguageTypeC_plus_plus);
-    if (state) {
-      auto *persistent_vars = llvm::cast<ClangPersistentVariables>(state);
-      clang_ast_importer = persistent_vars->GetClangASTImporter();
-    }
-
-    if (!clang_ast_importer) {
-      return;
-    }
-
     const char *const isa_name("__isa");
     const CompilerType isa_type =
         clang_ast_context->GetBasicType(lldb::eBasicTypeObjCClass);
     const char *const flags_name("__flags");
     const CompilerType flags_type =
         clang_ast_context->GetBasicType(lldb::eBasicTypeInt);
     const char *const reserved_name("__reserved");
     const CompilerType reserved_type =