Fix some corner case behavior in the new ORDER BY optimization logic.

Fix some corner case behavior in the new ORDER BY optimization logic.
Remove the SQLITE_OrderByIdx bit from the
SQLITE_TESTCTRL_OPTIMIZATIONS mask, since enabling it caused many
TH3 tests to fail when the NO_OPT configuration parameter was engaged,
and since there really isn't any need to turn that optimization off.
The SQLITE_OrderByIdxJoin bit remains.

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