Remove some methods from Database and make them internal to implementation

mailbox-core/src/main/java/org/briarproject/mailbox/core/db/Database.kt

@@ -2,7 +2,6 @@ package org.briarproject.mailbox.core.db
 
 import org.briarproject.mailbox.core.api.Contact
 import org.briarproject.mailbox.core.settings.Settings
-import java.sql.Connection
 
 interface Database : TransactionManager {
 
@@ -18,19 +17,6 @@ interface Database : TransactionManager {
     @Throws(DbException::class)
     fun close()
 
-    /**
-     * Aborts the given transaction - no changes made during the transaction
-     * will be applied to the database.
-     */
-    fun abortTransaction(connection: Connection)
-
-    /**
-     * Commits the given transaction - all changes made during the transaction
-     * will be applied to the database.
-     */
-    @Throws(DbException::class)
-    fun commitTransaction(connection: Connection)
-
     @Throws(DbException::class)
     fun getSettings(txn: Transaction, namespace: String): Settings
 

mailbox-core/src/main/java/org/briarproject/mailbox/core/db/JdbcDatabase.kt

@@ -219,7 +219,7 @@ abstract class JdbcDatabase(private val dbTypes: DatabaseTypes, private val cloc
         return connection
     }
 
-    override fun abortTransaction(connection: Connection) {
+    private fun abortTransaction(connection: Connection) {
         try {
             connection.rollback()
             connectionsLock.lock()
@@ -244,7 +244,7 @@ abstract class JdbcDatabase(private val dbTypes: DatabaseTypes, private val cloc
         }
     }
 
-    override fun commitTransaction(connection: Connection) {
+    private fun commitTransaction(connection: Connection) {
         try {
             connection.commit()
         } catch (e: SQLException) {