DELETE statement

Single-table delete ordered by a field that has a hash-type index
may cause an assertion failure or a crash.

An optimization added by the fix for the bug 36569 forced the
optimizer to use ORDER BY-compatible indices when applicable.

However, the existence of unsorted indices (HASH index algorithm
for some engines such as MEMORY/HEAP, NDB) was ignored.

The test_if_order_by_key function has been modified to skip
unsorted indices.