pgsql: Improve wording of some pg_upgrade failure reports.

Improve wording of some pg_upgrade failure reports.

Don't advocate dropping a whole table when dropping a column would
serve.  While at it, try to make the layout of these messages a
bit cleaner and more consistent.

Per suggestion from Daniel Gustafsson.  No back-patch, as we generally
don't like to churn translatable messages in released branches.

Discussion: https://postgr.es/m/2798740.1619622555@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/c9c37ae03fea0c8ad467392ddf03940b61974935

Modified Files
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src/bin/pg_upgrade/check.c   | 10 +++++-----
src/bin/pg_upgrade/version.c | 26 ++++++++++++++------------
2 files changed, 19 insertions(+), 17 deletions(-)