pgsql: Grab the low-hanging fruit from forcing USE_FLOAT8_BYVAL to true

Grab the low-hanging fruit from forcing USE_FLOAT8_BYVAL to true.

Remove conditionally-compiled code for the other case.

Replace uses of FLOAT8PASSBYVAL with constant "true", mainly because
it was quite confusing in cases where the type we were dealing with
wasn't float8.

I left the associated pg_control and Pg_magic_struct fields in place.
Perhaps we should get rid of them, but it would save little, so it
doesn't seem worth thinking hard about the compatibility implications.
I just labeled them "vestigial" in places where that seemed helpful.

Author: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Reviewed-by: Peter Eisentraut <peter(at)eisentraut(dot)org>
Discussion: https://postgr.es/m/1749799.1752797397@sss.pgh.pa.us

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/ee54046601de2d14ca9107ba04c50178d9b52fe6

Modified Files
--------------
contrib/btree_gist/btree_time.c | 51 ++++++++----------
contrib/btree_gist/btree_ts.c | 39 ++++++--------
src/backend/access/common/tupdesc.c | 2 +-
src/backend/access/index/indexam.c | 5 --
src/backend/access/transam/xlog.c | 20 +------
src/backend/catalog/genbki.pl | 3 +-
src/backend/optimizer/plan/planagg.c | 2 +-
src/backend/optimizer/plan/planner.c | 4 +-
src/backend/parser/parse_node.c | 2 +-
src/backend/rewrite/rewriteSearchCycle.c | 2 +-
src/backend/utils/adt/arrayfuncs.c | 6 +--
src/backend/utils/adt/int8.c | 75 +++++----------------------
src/backend/utils/adt/numeric.c | 74 ++++++--------------------
src/backend/utils/adt/orderedsetaggs.c | 2 +-
src/backend/utils/adt/rangetypes_typanalyze.c | 2 +-
src/backend/utils/fmgr/fmgr.c | 35 -------------
src/bin/initdb/initdb.c | 3 --
src/bin/pg_resetwal/pg_resetwal.c | 2 +-
src/include/c.h | 8 +--
src/include/catalog/pg_type.dat | 16 +++---
src/include/fmgr.h | 2 +-
src/include/postgres.h | 58 ++-------------------
22 files changed, 100 insertions(+), 313 deletions(-)