pgsql: Temporarily remove a test case that hits an unfixed bug

Temporarily remove a test case that hits an unfixed bug

Buildfarm animal trilobite turned red because the test that is
being removed crashes due to a long-standing bug in how
ri_FetchPreparedPlan() handles an invalid SPI plan, which the test
started reaching after 6aecabcd5ed made it go through the SPI path
and which CLOBBER_CACHE_ALWAYS exposes. Fixing that bug will take
some time, so in the meantime remove the test case so the buildfarm
can turn green and other committers are not distracted by this.

The test will be re-added with the commit to fix the bug.

Reported-by: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>
Reported-by: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Discussion: https://postgr.es/m/3043944.1792163844@sss.pgh.pa.us
Discussion: https://posgre.es/m/CA+HiwqE=QFc7xS72xZ5scFNUbLdOCJyvew+3toLebsWipJOqnQ@mail.gmail.com
Backpatch-through: 19

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/f52d405113c83f691fffac261bfec297209c21b4

Modified Files
--------------
src/test/regress/expected/foreign_key.out | 27 ---------------------------
src/test/regress/sql/foreign_key.sql | 22 ----------------------
2 files changed, 49 deletions(-)