pgsql: Remove COMMIT_TS_SETTS record.

Remove COMMIT_TS_SETTS record.

Commit 438fc4a39c prevented the WAL replay from writing
COMMIT_TS_SETTS record. By this change there is no code that
generates COMMIT_TS_SETTS record in PostgreSQL core.
Also we can think that there are no extensions using the record
because we've not received so far any complaints about the issue
that commit 438fc4a39c fixed. Therefore this commit removes
COMMIT_TS_SETTS record and its related code. Even without
this record, the timestamp required for commit timestamp feature
can be acquired from the COMMIT record.

Bump WAL page magic.

Reported-by: lx zou <zoulx1982(at)163(dot)com>
Author: Fujii Masao
Reviewed-by: Alvaro Herrera
Discussion: https://postgr.es/m/16931-620d0f2fdc6108f1@postgresql.org

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/08aa89b326261b669648df97d4f2a6edba22d26a

Modified Files
--------------
src/backend/access/rmgrdesc/committsdesc.c | 27 -------------
src/backend/access/transam/commit_ts.c | 64 +-----------------------------
src/backend/access/transam/twophase.c | 2 +-
src/backend/access/transam/xact.c | 4 +-
src/include/access/commit_ts.h | 3 +-
src/include/access/xlog_internal.h | 2 +-
6 files changed, 6 insertions(+), 96 deletions(-)