Rename SkFontHost_none.cpp to SkFontMgr_empty_factory.

When the current function was added in
https://skia.googlesource.com/skia/+/070da5edcb1c6e9b9507f06a5e2c270e1c1fd796%5E%21/#F3
the SkFontHost was still alive and well. Now that this file no
longer contains any SkFontHost related code, rename the file for
clarity and uniformity.

Review URL: https://codereview.chromium.org/1196313003
1 file changed