This extracts ole replacement code from FlyFrameOLEMath() and makes
FlyFrameOLE() use it as well, as the later didn't write png replacement,
just wmf one. Also remove FlyFrameOLEData(), which is now unused (it was
only used by math, but math export returns earlier).

Change-Id: I5e88708cdad1468ccbc5c3c8bb77521785822832