Revert "ensure topData->m_importers/topData->m_importedContexts is not nullptr, this fix crash while finding usage of var/function/class."

This reverts commit 3d2501acb133d5a43aad09cd370a44c3791a9262.

Sorry for this commit. With many tests by big projects, I found that this patch does not work. I am still working on this bug.