For UPDATE and DELETE, use OP_DeferredSeek always. If the seek must later

For UPDATE and DELETE, use OP_DeferredSeek always.  If the seek must later
be resolved, add the OP_FinishSeek opcode after all WHERE clause terms have
been processed.  This obviates the need for the WHERE_SEEK_TABLE and
WHERE_SEEK_UNIQ_TABLE flags to sqlite3WhereBegin() and the ensuing
complication, and it allows the covering index optimization to be used
further into WHERE clause processing.

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