PreparedStatement deprecate pending_prepared_stream

[suketa]

By removing duckdb_pending_prepared_stream and using duckdb_pending_prepared instead,
PendingResult.new(prepared_statement, true) and PendingResult.new(prepared_statement, false), PendingResult.new(prepared_statement) are same.

So, pending_prepared_stream and pending_prepared method are same.

    def pending_prepared
      PendingResult.new(self)
    end

    def pending_prepared_stream
      PendingResult.new(self, true)
    end