Remove orphaned expected-result file.

This should have been removed in 43e08419, which removed the
corresponding spec file.  Noted while fooling about with the
isolationtester.

src/test/isolation/expected/insert-conflict-toast_1.out

-Parsed test spec with 3 sessions
-
-starting permutation: s2insert s3insert s1commit
-pg_advisory_xact_lock
-
-               
-step s2insert: 
-  INSERT INTO ctoast (key, val) VALUES (1, ctoast_large_val()) ON CONFLICT DO NOTHING;
- <waiting ...>
-step s3insert: 
-  INSERT INTO ctoast (key, val) VALUES (1, ctoast_large_val()) ON CONFLICT DO NOTHING;
- <waiting ...>
-step s1commit: COMMIT;
-step s3insert: <... completed>
-step s2insert: <... completed>