pgsql: Make FSM test portable.

Make FSM test portable.

In b0eaa4c51b, we allow FSM to be created only after 4 pages.  One of the
tests check the FSM contents and to do that it populates many tuples in
the relation.  The FSM contents depend on the availability of freespace in
the page and it could vary because of the alignment of tuples.

This commit removes the dependency on FSM contents.

Author: Amit Kapila
Discussion: https://postgr.es/m/CAA4eK1KADF6K1bagr0--mGv3dMcZ%3DH_Z-Qtvdfbp5PjaC6PJJA%40mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/08ecdfe7e5e0a31efbe1d58fefbe085b53bc79ca

Modified Files
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contrib/pageinspect/expected/page.out | 23 +++++------------------
contrib/pageinspect/sql/page.sql      |  3 ++-
2 files changed, 7 insertions(+), 19 deletions(-)