pgsql: Remove some more "snapshot too old" vestiges.

Remove some more "snapshot too old" vestiges.

Commit f691f5b8 removed the logic, but left behind some now-useless
Snapshot arguments to various AM-internal functions, and missed a couple
of comments.

Reported-by: Peter Geoghegan <pg(at)bowt(dot)ie>
Discussion: https://postgr.es/m/CAH2-Wznj9qSNXZ1P1uWTUD_FeaTezbUazb416EPwi4Qr_jR_6A%40mail.gmail.com

Branch
------
master

Details
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https://git.postgresql.org/pg/commitdiff/9f0602539db4573b89c09abab666e85b653940bd

Modified Files
--------------
contrib/amcheck/verify_nbtree.c | 2 +-
src/backend/access/brin/brin.c | 21 ++++++++---------
src/backend/access/brin/brin_revmap.c | 8 +++----
src/backend/access/common/toast_internals.c | 3 +--
src/backend/access/gin/ginbtree.c | 2 +-
src/backend/access/gin/gindatapage.c | 7 +++---
src/backend/access/gin/ginget.c | 28 +++++++++++------------
src/backend/access/gin/gininsert.c | 2 +-
src/backend/access/heap/vacuumlazy.c | 4 ----
src/backend/access/nbtree/nbtinsert.c | 4 ++--
src/backend/access/nbtree/nbtpage.c | 3 +--
src/backend/access/nbtree/nbtsearch.c | 35 +++++++++--------------------
src/backend/access/spgist/spgscan.c | 7 +++---
src/include/access/brin_revmap.h | 4 ++--
src/include/access/gin_private.h | 4 ++--
src/include/access/nbtree.h | 7 +++---
16 files changed, 56 insertions(+), 85 deletions(-)