pgsql: Remove duplicated comment block in event_trigger.c

Remove duplicated comment block in event_trigger.c

The reasons why event triggers are disabled in standalone mode are
documented in the code path of ddl_command_start, and other places
checking if standalone mode is enabled or not mention to refer to the
comment for ddl_command_start, except for table_rewrite that duplicated
the same explanation.

Reported-by: David G. Johnston
Discussion: https://postgr.es/m/CAKFQuwYqHtXpvr2mBJRwH9f+Y5y1GXw3rhbaAu0Dk2MoNevsmA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/ff87fabef20ef40c8438e25fe28e9159f874183d

Modified Files
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src/backend/commands/event_trigger.c | 16 ++--------------
1 file changed, 2 insertions(+), 14 deletions(-)