pgsql: Simplify redundant current_database() subqueries in stats.sql re

Simplify redundant current_database() subqueries in stats.sql regression test

Previously the stats.sql regression test used conditions like
"datname = (SELECT current_database())" to check the current database name.

The subquery is unnecessary, so this commit simplifies these expressions to
"datname = current_database()".

Author: Chao Li <lic@highgo.com>
Reviewed-by: Fujii Masao <masao.fujii@gmail.com>
Discussion: https://postgr.es/m/A1535A8F-65AF-4C3D-ACBE-25891CB5D38B@gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/d78a4f0bf058906c5cfd25c815ccbdf18013b312

Modified Files
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src/test/regress/expected/stats.out | 12 ++++++------
src/test/regress/sql/stats.sql      | 12 ++++++------
2 files changed, 12 insertions(+), 12 deletions(-)