DDL - Refactor DDL for Postgres and YugabyteDB to just create a default partition table

Removes the need and use of  PostgresPlatform.tablePartitionsExist() and PostgresPlatform.tablePartitionInit() altogether.

ebean-api/src/main/java/io/ebean/config/dbplatform/DatabasePlatform.java

@@ -802,20 +802,6 @@ public class DatabasePlatform {
     }
   }
 
-  /**
-   * Return true if partitions exist for the given table.
-   */
-  public boolean tablePartitionsExist(Connection connection, String table) throws SQLException {
-    return true;
-  }
-
-  /**
-   * Return the SQL to create an initial partition for the given table.
-   */
-  public String tablePartitionInit(String tableName, PartitionMode mode) {
-    return null;
-  }
-
   /**
    * Escapes the like string for this DB-Platform
    */