doc(semver): remove mention of deprecated tool rust-semverver

See also

* https://rust-lang.zulipchat.com/#narrow/stream/242791-t-infra/topic/Creating.20a.20release.20for.20rust-semverver
* rust-lang/team#1390
* rust-lang/rust-semverver#373

Author: weihanglo

src/doc/src/reference/semver.md

@@ -14,11 +14,7 @@ negatively affect the runtime behavior, and for those cases it is usually a
 judgment call by the project maintainers whether or not it is a
 SemVer-incompatible change.
 
-See also [rust-semverver], which is an experimental tool that attempts to
-programmatically check compatibility rules.
-
 [Change categories]: #change-categories
-[rust-semverver]: https://github.com/rust-lang/rust-semverver
 [SemVer compatibility]: resolver.md#semver-compatibility
 
 ## Change categories