Make float exponent output on Windows look the same as elsewhere.

Make float exponent output on Windows look the same as elsewhere.

Windows, alone among our supported platforms, likes to emit three-digit
exponent fields even when two digits would do.  Adjust such results to
look like the way everyone else does it.  Eliminate a bunch of variant
expected-output files that were needed only because of this quirk.

Discussion: https://postgr.es/m/2934.1539122454@sss.pgh.pa.us