chore(model): Remove the unused transactionAsync() function

This is a follow-up to f7dd719.

Signed-off-by: Sebastian Schuberth <sebastian@doubleopen.org>

model/src/main/kotlin/utils/DatabaseUtils.kt

@@ -26,13 +26,10 @@ import java.util.concurrent.ConcurrentHashMap
 
 import javax.sql.DataSource
 
-import kotlinx.coroutines.Deferred
-
 import org.apache.logging.log4j.kotlin.logger
 
 import org.jetbrains.exposed.sql.Database
 import org.jetbrains.exposed.sql.Transaction
-import org.jetbrains.exposed.sql.transactions.experimental.suspendedTransactionAsync
 import org.jetbrains.exposed.sql.transactions.transaction
 
 import org.ossreviewtoolkit.model.config.PostgresConnection
@@ -118,12 +115,6 @@ object DatabaseUtils {
      */
     fun <T> Database.transaction(statement: Transaction.() -> T): T = transaction(this, statement)
 
-    /**
-     * Start a new asynchronous transaction to execute the given [statement] on this [Database].
-     */
-    suspend fun <T> Database.transactionAsync(statement: suspend Transaction.() -> T): Deferred<T> =
-        suspendedTransactionAsync(db = this, statement = statement)
-
     /**
      * Add a property with the given [key] and [value] to the [HikariConfig]. If the [value] is *null*, this
      * function has no effect. (It is not specified how the database driver deals with *null* values in its