pgsql: Simplify multixact freezing a bit

Simplify multixact freezing a bit

Testing for abortedness of a multixact member that's being frozen is
unnecessary: we only need to know whether the transaction is still in
progress or committed to determine whether it must be kept or not.  This
let us simplify the code a bit and avoid a useless TransactionIdDidAbort
test.

Suggested by Andres Freund awhile back.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/c2581794f37e76c910eb91f1bf1f1e581123abd6

Modified Files
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src/backend/access/heap/heapam.c |   56 ++++++++++++++++----------------------
1 file changed, 23 insertions(+), 33 deletions(-)