- remove PD_FIRST and GetFirstFmt:
  This flag makes no sense at all, since there are no "first-only"
  page styles (while there are left-only/right-only).
- instead add a parameter to GetLeftFmt/GetRightFmt to request a
  first page format, if such exists and is not shared
(regression from 02a934d0
 and fa0f42ba)

Change-Id: I4d50c2c0cc4f3cf231eacba891df22d0bcf6c4df