Drop Neon-specific spgist regression test change

The original purpose for this change was to keep test_pg_regress with
the way that Neon handles unlogged relations. Instead, we can just
filter the files the test checks against.

src/test/regress/expected/spgist.out

@@ -94,6 +94,3 @@ select box(point(i,j))
   from generate_series(1,100,5) i,
        generate_series(1,10,5) j;
 -- leave this table around, to help in testing dump/restore
--- NEON: In Neon unlogged tables are wiped away on node restart
--- so drop the table to keep Neon tests clean.
-drop table spgist_unlogged_tbl;

src/test/regress/sql/spgist.sql

@@ -89,6 +89,3 @@ select box(point(i,j))
   from generate_series(1,100,5) i,
        generate_series(1,10,5) j;
 -- leave this table around, to help in testing dump/restore
--- NEON: In Neon unlogged tables are wiped away on node restart
--- so drop the table to keep Neon tests clean.
-drop table spgist_unlogged_tbl;