pgsql: Remove unneeded header declarations in multixact.c

Remove unneeded header declarations in multixact.c

Two header declarations were related to SQL-callable functions, that
should have been cleaned up in df9133fa6384. Some more includes can be
removed on closer inspection, so let's clean up these as well, while on
it.

Reported-by: Tom Lane <tgl@sss.pgh.pa.us>
Discussion: /messages/by-id/345438.1755524834@sss.pgh.pa.us

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/24e71d53f88e1a37506cf1c9967b6db5d685f249

Modified Files
--------------
src/backend/access/transam/multixact.c | 5 -----
1 file changed, 5 deletions(-)