Move public tx listing API to host DB query (#1900)

* add new fetch transactions API to host interface 
* refactor tenscan API to call new host interface
* remove redundant enclave client API

design/host/host_db_requirements.md

@@ -122,7 +122,7 @@ but on mainnet this won't be possible, so we need to store the `tx_count` in thi
 `ExtBatch.TxHashes` and expose a new Enclave API to retrieve this.
 
 ```sql
-create table if not exists transactions_host
+create table if not exists transaction_host
 (
     hash           binary(32) primary key,
     b_sequence     int REFERENCES batch_host

go/common/enclave.go

@@ -142,9 +142,6 @@ type EnclaveScan interface {
 	// GetCustomQuery returns the data of a custom query
 	GetCustomQuery(ctx context.Context, encryptedParams EncryptedParamsGetStorageAt) (*responses.PrivateQueryResponse, SystemError)
 
-	// GetPublicTransactionData returns a list of public transaction data
-	GetPublicTransactionData(ctx context.Context, pagination *QueryPagination) (*TransactionListingResponse, SystemError)
-
 	// EnclavePublicConfig returns network data that is known to the enclave but can be shared publicly
 	EnclavePublicConfig(context.Context) (*EnclavePublicConfig, SystemError)
 }