pgsql: Doc: clean up some places that mentioned template1 but not templ

Doc: clean up some places that mentioned template1 but not template0.

Improve old text that wasn't updated when we added template0 to
the standard database set.

Per suggestion from P. Luzanov.

Discussion: https://postgr.es/m/163583775122.675.3700595100340939507@wrigleys.postgresql.org

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/7d9ec0754afeabb9f336c5220ef415c3ea27a0b6

Modified Files
--------------
doc/src/sgml/manage-ag.sgml  | 14 ++++++++++----
doc/src/sgml/ref/initdb.sgml | 19 +++++++++++--------
doc/src/sgml/runtime.sgml    |  8 ++++----
3 files changed, 25 insertions(+), 16 deletions(-)