Support MySQL 5.7

Caused by: com.mysema.query.QueryException: Caught SQLException for delete from `CONTENTPROPERTIES`
where `CONTENTPROPERTIES`.`PROPERTYID` in (select `PROPERTY_ID`
from (select `answerProperties`.`PROPERTYID` as `PROPERTY_ID`
from `CONTENT` `answers`
join `CONTENTPROPERTIES` `answerProperties`
on `answerProperties`.`CONTENTID` = `answers`.`CONTENTID`
left join (select `questionProperties`.`LONGVAL` as `ANSWER_ID`
from `CONTENT` `questions`
join `CONTENTPROPERTIES` `questionProperties`
on `questionProperties`.`CONTENTID` = `questions`.`CONTENTID`
where `questions`.`PLUGINKEY` = 'com.atlassian.confluence.plugins.confluence-questions:question' and `questions`.`PREVVER` is null and `questionProperties`.`PROPERTYNAME` = 'accepted') as `ACCEPTED_ANSWER_IDS`
on `answers`.`CONTENTID` = `ANSWER_ID`
where `answers`.`PLUGINKEY` = 'com.atlassian.confluence.plugins.confluence-questions:answer' and `answers`.`PREVVER` is null and `answerProperties`.`PROPERTYNAME` = 'accepted' and `ANSWER_ID` is null) as `TMP`)
    at com.mysema.query.sql.DefaultSQLExceptionTranslator.translate(DefaultSQLExceptionTranslator.java:38)
    at com.mysema.query.sql.Configuration.translate(Configuration.java:451)
    at com.mysema.query.sql.dml.SQLDeleteClause.execute(SQLDeleteClause.java:169)
    at com.atlassian.confluence.plugins.questions.internal.upgrade.DuplicatedAcceptedAnswersRemover.deleteDuplicatedAcceptedAnswers(DuplicatedAcceptedAnswersRemover.java:83)
...
    at com.atlassian.activeobjects.internal.AbstractActiveObjectsFactory.create(AbstractActiveObjectsFactory.java:67)
    at com.atlassian.activeobjects.internal.DelegatingActiveObjectsFactory.create(DelegatingActiveObjectsFactory.java:32)
    at com.atlassian.activeobjects.osgi.TenantAwareActiveObjects$1$1$1.call(TenantAwareActiveObjects.java:91)
    ... 6 more
Caused by: java.sql.SQLException: You can't specify target table 'CONTENTPROPERTIES' for update in FROM clause