Omit the check for conflicting shared-cache locks in sqlite3Prepare() if the

Omit the check for conflicting shared-cache locks in sqlite3Prepare() if the
database connection uses no shared cache.  We might be able to go back and
remove this code completely, due to the newer Schema.iGeneration logic, but
that will take more analysis.  This check-in gives the speed benefit but not
the reduction in code size.

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