pgsql: Remove pg_upgrade support for upgrading from pre-9.2 servers.

Remove pg_upgrade support for upgrading from pre-9.2 servers.

Per discussion, we'll limit support for old servers to those branches
that can still be built easily on modern platforms, which as of now
is 9.2 and up.

Discussion: https://postgr.es/m/2923349.1634942313@sss.pgh.pa.us

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/e469f0aaf3c586c8390bd65923f97d4b1683cd9f

Modified Files
--------------
doc/src/sgml/ref/pgupgrade.sgml  |  17 +----
src/bin/pg_upgrade/check.c       |  28 +-------
src/bin/pg_upgrade/info.c        |  24 ++-----
src/bin/pg_upgrade/pg_upgrade.h  |  16 +----
src/bin/pg_upgrade/relfilenode.c |  12 +---
src/bin/pg_upgrade/server.c      |  14 +---
src/bin/pg_upgrade/tablespace.c  |  22 ++-----
src/bin/pg_upgrade/test.sh       |   3 -
src/bin/pg_upgrade/version.c     | 134 +++++++--------------------------------
9 files changed, 43 insertions(+), 227 deletions(-)