Centralize the max glyph dimension

Over several refactorings the max glyph dimension has become
a constant. Simplify the code by removing variables that can
only be constant.

Change-Id: I65800a5ec1dfd4de5337f2f37348bd0eb101cc3e
Reviewed-on: https://skia-review.googlesource.com/154123
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Herb Derby <herb@google.com>
8 files changed