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

Author: tglsfdc