Log Message:
harfbuzz: Update to 2.6.1

Overview of changes leading to 2.6.1
Thursday, August 22, 2019

    Fix regression with hb_font_create_sub_font scaling introduced in 2.6.0.
    Change interpretation of font PTEM size / CoreText font size handling.
    See #1484
    hb-ot-font: Prefer symbol cmap subtable if present.
    Apply 'dist'/'abvm'/'blwm' features to all scripts.
    Drop experimental DirectWrite API.