Correction of U.dpi to hold actual monitor DPI. Simplify font sizing by
omitting DPI as API argument, always using 72 internally.
See D15961 for more details.
Differential Revision: https://developer.blender.org/D15961
Reviewed by Campbell Barton
Note that lib_override functions have kept the unused argument,
but this may be removed too. It impacts many lib_override functions
so this can be handled separately.
