pgsql: Fix "sesssion" typo

Fix "sesssion" typo

It was introduced alongside replication origins, by commit
5aa2350426c, so backpatch to 9.5.

Pointed out by Fujii Masao

Branch
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REL9_5_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/aea76d128ad85f38aa0f4255fb9d46d95b835755

Modified Files
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src/backend/access/transam/xact.c        |   20 ++++++++++----------
src/backend/access/transam/xloginsert.c  |    6 +++---
src/backend/replication/logical/origin.c |   26 +++++++++++++-------------
src/include/replication/origin.h         |    6 +++---
4 files changed, 29 insertions(+), 29 deletions(-)