Inconsistent handling of spring.datasource.jmx-enabled

[snicoll]

I've already raised and auto-declined this in #9271

There is a spring.datasource.tomcat.jmx-enabled property so looks like I was wrong when I closed it.

Besides, spring.datasource.jmx-enabled has some very specific description that imply this is generic and used by all connection pools we know that have JMX support. It isn't, it is specific to Tomcat.

[snicoll]

We've discussed and we decided to move to the tomcat property and drop the reference to the outdated spring.datasource.jmx-enabled property.