Mention struct-like variants in enums2 hint instead of anonymous structs

[orzechow]

The current hint of the enums2 exercise uses an outdated term for struct-like enum variants, which is confusing to Rust newbies:

You can create enumerations that have different variants with different types such as anonymous structs, structs, a single string, tuples, no data, etc.

The term anonymous struct seems outdated. It's neither mentioned in the Rust book on structs or enums, nor the references on structs or enums.
A web search rather points to a Rust Forum thread hinting

Don’t assume that there is such a thing as “the anonymous struct feature” at all

The only place I found this term, is in the Rust docs on enums, but not in the docs on structs.
It seems like Rust used this term once, but not anymore. See also #1204 and the 2018 edition Rust book on enums.

Instead the book on enums now calls it named fields, like a struct.
The reference on enums uses the term struct-like enum variant.

Therefore, I'd suggest updating this hint to struct-like enum variants.

[orzechow]

See also my PR to improve the Rust docs on that matter:

• Use the term struct-like data instead of anonymous structs for data of struct-like enum variants rust#152530