pgsql: Remove abstime, reltime, tinterval tables from old regression da

Remove abstime, reltime, tinterval tables from old regression databases.

In the back branches, drop these tables after the regression tests are
done with them. This fixes failures of cross-branch pg_upgrade testing
caused by these types having been removed in v12. We do lose the ability
to test dump/restore behavior with these types in the back branches, but
the actual loss of code coverage seems to be nil given that there's nothing
very special about these types.

Discussion: /messages/by-id/20181009192237.34wjp3nmw7oynmmr@alap3.anarazel.de

Branch
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REL9_6_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/2ad422ce10a4c84cea2fede1cdfc6831940707f0

Modified Files
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src/test/regress/expected/horology.out | 7 +++++++
src/test/regress/expected/sanity_check.out | 3 ---
src/test/regress/sql/horology.sql | 9 +++++++++
3 files changed, 16 insertions(+), 3 deletions(-)