Revert ill-considered change in pg_resetwal output.

Revert ill-considered change in pg_resetwal output.

Commit 31dcfae83 changed one pg_resetwal output string, and a
corresponding test in pg_upgrade, without sufficient thought for
the consequences.  We can't change that output without creating
hazards for cross-version upgrades, since pg_upgrade needs to be able
to read the output of several different versions of pg_resetwal.
There may well be external tools with the same requirement.

For the moment, just revert those two changes.  What we really
ought to do here is have a separate, stable, easily machine-readable
output format for pg_resetwal and pg_controldata, as proposed
years ago by Alvaro.  Once that's in place and tools no longer
need to depend on the exact spelling of the human-readable output,
we can put back this change.

Discussion: https://postgr.es/m/fbea8c6f-415a-bad9-c3de-969c40d08a84@dunslane.net