pgsql: Clean up some variable names in ri_triggers.c

Clean up some variable names in ri_triggers.c

There was a mix of old_slot/oldslot, new_slot/newslot. Since we've
changed everything from row to slot, we might as well take this
opportunity to clean this up.

Also update some more comments for the slot change.

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0a271df705c98c1cc617078ebd069cf080fa5a16

Modified Files
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src/backend/utils/adt/ri_triggers.c | 70 ++++++++++++++++++-------------------
1 file changed, 35 insertions(+), 35 deletions(-)