pgsql: doc: remove incorrect grammar for ALTER EVENT TRIGGER

doc: remove incorrect grammar for ALTER EVENT TRIGGER

The Parameters subsection had an extra TRIGGER in the grammar
for DISABLE/ENABLE which is incorrect.  Backpatch down to all
supported versions since it's been like this all along.

Discussion: https://postgr.es/m/0AFB171E-7E78-4A90-A140-46AB270212CA@yesql.se
Backpatch-through: v12

Branch
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REL_13_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/a0cffcfffd11b0ea7662f47cfd4d225150e55dbf

Modified Files
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doc/src/sgml/ref/alter_event_trigger.sgml | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)