revert: "Add MySQL implementation (#803)" (#807)

This reverts commit 98710d8.

core/src/main/scala/akka/persistence/jdbc/state/DurableStateQueries.scala

@@ -39,7 +39,6 @@ import akka.persistence.jdbc.config.DurableStateTableConfiguration
   lazy val sequenceNextValUpdater = slickProfileToSchemaType(profile) match {
     case "H2"       => new H2SequenceNextValUpdater(profile, durableStateTableCfg)
     case "Postgres" => new PostgresSequenceNextValUpdater(profile, durableStateTableCfg)
-    case "MySQL"    => new MySQLSequenceNextValUpdater(profile, durableStateTableCfg)
     case _          => ???
   }
 

core/src/main/scala/akka/persistence/jdbc/state/SequenceNextValUpdater.scala

@@ -51,19 +51,3 @@ import slick.sql.SqlStreamingAction
 
   def getSequenceNextValueExpr() = sql"""#$nextValFetcher""".as[String]
 }
-
-/**
- * INTERNAL API
- */
-@InternalApi private[jdbc] class MySQLSequenceNextValUpdater(
-    profile: JdbcProfile,
-    val durableStateTableCfg: DurableStateTableConfiguration)
-    extends SequenceNextValUpdater {
-  import profile.api._
-  private val schema = durableStateTableCfg.schemaName.map(n => s"'$n'").getOrElse("DATABASE()")
-  // Note: for actual MySQL servers (i.e. not MariaDB) the variable information_schema_stats_expiry should be set to zero.
-  final val nextValFetcher =
-    s"""(SELECT AUTO_INCREMENT FROM information_schema.tables WHERE table_name = '${durableStateTableCfg.tableName}' AND table_schema = ${schema})"""
-
-  def getSequenceNextValueExpr() = sql"""#$nextValFetcher""".as[String]
-}