Remove remaining code that was deprecated in 2.5

[wilkinsona]

While looking at #30435, I noticed that the DB initialization related properties on DataSourceProperties that were deprecated in 2.5 have not been removed. I suspect they were missed during #29290 as they're configuration properties so there was no "deprecated since 2.5.0 for removal in 2.7.0" to look for.

[IAmSSH]

Hi @wilkinsona
Can I work on this issue?
Though the issue is not labeled explicitly for first-timers, I would like to give it a try if you don't mind.
Could you perhaps provide a little bit of guidance about what needs to be done?

[wilkinsona]

Thanks for the offer, @IAmSSH. If you’d like to work on an issue where we provide some guidance, please watch for one labelled as ideal for contribution or, if you haven’t contributed before, first-timers only.

[snicoll]

A note that there are a number of tests that are still relying on spring.datasource.intialization-mode. When removing the properties for this, we should review manual metadata as well.