Our current DDL only allows a database name to be specified in COMMENT
ON DATABASE, which Andrew Dunstan reports to make this test fail on the
buildfarm.  Remove the line until we gain a DDL command that allows the
current database to be operated on without having the specify it by
name.

Backpatch to 9.5, where these tests appeared.

Discussion: https://postgr.es/m/e6084b89-07a7-7e57-51ee-d7b8fc9ec864@2ndQuadrant.com