pgsql: Use ExplainPropertyInteger for queryid in EXPLAIN

Use ExplainPropertyInteger for queryid in EXPLAIN

This saves a few lines of code.  Also add a comment to mention why we use
ExplainPropertyInteger instead of ExplainPropertyUInteger given that
queryid is a uint64 type.

Author: David Rowley
Reviewed-by: Julien Rouhaud
Discussion: https://postgr.es/m/CAApHDvqhSLYpSU_EqUdN39w9Uvb8ogmHV7_3YhJ0S3aScGBjsg@mail.gmail.com
Backpatch-through: 14, where this code was originally added

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/4a3d806f38f99fecf8f2a2bf7990a7ebea9b6c63

Modified Files
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src/backend/commands/explain.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)