De-virtualize CPDFSDK_AnnotHandlerMgr
De-virtualize CPDFSDK_AnnotHandlerMgr

It has no sub-classes or super-classes, so no need for virtual.

Review-Url: https://codereview.chromium.org/2365383003

DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium,DrAlexx/pdfium