Incoming breakage: Replace an invalid #[deprecated] attribute with a doc comment

[fmease]

• I agree to follow the project's code of conduct.
• I added an entry to CHANGES.md if knowledge of this change could be valuable to users.

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#[deprecated] attributes on impl blocks do not have any effect and normally the deny-by-default lint useless_deprecated would be triggered with the message this #[deprecated] annotation has no effect.
However, there is a bug in the current version of the Rust compiler that makes it ignore the attribute entirely if it is malformed
which is the case for the #[deprecated] attached to the From impl for GeometryCollection (the version is not surrounded by double quotes).
I've replaced the attribute with a documentation comment similar to the one for the softly deprecated associated function GeometryCollection::new_from.

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The compiler bug is about to be fixed (rust-lang/rust#104148) and the malformed attribute will soon become a hard error.
This future breakage was found with the help of crater (see the build log).

[michaelkirk]

bors r+

Thanks @fmease!

[bors]

Build succeeded:

• ci result

[michaelkirk]

A reminder to future us... assuming rust-lang/rust#104148 is merged soon, I think this change would hit beta 2022-12-15 and stable 2023-1-26.

People will see a failure like this:

[INFO] [stderr]     Checking geo-types v0.7.7
[INFO] [stdout] error: expected `,`, found `.`
[INFO] [stdout]    --> /opt/rustwide/cargo-home/registry/src/github.com-1ecc6299db9ec823/geo-types-0.7.7/src/geometry/geometry_collection.rs:111:25
[INFO] [stdout]     |
[INFO] [stdout] 111 | #[deprecated(since = 0.7.5, note = "Use `GeometryCollection::from(vec![geom])` instead.")]
[INFO] [stdout]     |                         ^ expected `,`
[INFO] [stdout] 

In which case they just need to update geo-types to something newer than geo-types-0.7.7