Set tx field to none if `include_raw` is false

Set tx field to none if `include_raw` is false

`del_tx` pulls the TransactionDetails object using
`select_transaction_details_by_txid` method which gets the transaction
details' data with a non-None transaction field even if the
`include_raw` argument is `false`. So it becomes necessary to Set
the transaction field in transactiondetails to None in `del_tx`, when
we make a call to it with `include_raw=false`.