pgsql: revert: add transaction processing chapter with internals info

revert:  add transaction processing chapter with internals info

This doc patch (master hash 66bc9d2d3e) was decided to be too
significant for backpatching, so reverted in all but master.  Also fix
SGML file header comment in master.

Reported-by:    Peter Eisentraut

Discussion: https://postgr.es/m/c6304b19-6ff7-f3af-0148-cf7aa7e2fbfd@enterprisedb.com

Backpatch-through: 11

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/af6a76931634780fd5a67f2e1dee84a269e1f14a

Modified Files
--------------
doc/src/sgml/catalogs.sgml              |   7 +-
doc/src/sgml/config.sgml                |   6 +-
doc/src/sgml/filelist.sgml              |   1 -
doc/src/sgml/monitoring.sgml            |   3 +-
doc/src/sgml/pgrowlocks.sgml            |   3 +-
doc/src/sgml/postgres.sgml              |   1 -
doc/src/sgml/ref/release_savepoint.sgml |  62 ++++------
doc/src/sgml/ref/rollback.sgml          |   8 +-
doc/src/sgml/ref/rollback_to.sgml       |   5 +-
doc/src/sgml/wal.sgml                   |   6 +-
doc/src/sgml/xact.sgml                  | 200 --------------------------------
11 files changed, 36 insertions(+), 266 deletions(-)