Remove integration for REST Docs' REST Assured support until REST Assured supports Groovy 5

[wilkinsona]

Support for REST Assured is going to be removed from Spring REST Docs as it doesn't support Groovy 5. Boot's integration needs to be removed as well.

[likhith5697]

Hi @wilkinsona 👋

I’ve opened PR #47692 to remove the REST Docs’ REST Assured integration as discussed.
All related classes and documentation references were updated accordingly.

Please review when convenient — thank you!