pgsql: Update obsolete comment.

Update obsolete comment.

Somebody didn't bother to fix this comment while adding foreign table
support to the code below it.

In passing, remove the explicit calling-out of relkind letters, which adds
complexity to the comment but doesn't help in understanding the code.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/a75b08066ab4b426b1bd056fed81302e5a5d5371

Modified Files
--------------
src/bin/pg_dump/pg_dump.c |    6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)