Clean up for tinyformat version 1.2

This is just to remove the workarounds that had to be added before this bug was fixed on the tinyformat end.

Commit message:

The new version of tinyformat should fix the "%+d" issue on OSX, so
re-enabled the test just to be sure, and remove old workaround code in
oiiotool.  Also a tiny change to align with tagged 1.2 version of
tinyformat.