Remove _FX_USEGASFONTMGR_ as it is always defined
Remove _FX_USEGASFONTMGR_ as it is always defined

R=tsepez@chromium.org

Review URL: https://codereview.chromium.org/1749793002 .

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