Make GrFontScaler not be ref-counted

This object is made invalid when the SkGlyphCache that it points to is destroyed.

BUG=chromium:608566
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1982303002

Review-Url: https://codereview.chromium.org/1982303002
2 files changed