Remove the link to the Scaladoc of UndefinedBehaviorError.

It is not part of the public API anymore, so it has no Scaladoc.

Author: sjrd

doc/semantics.md

@@ -124,9 +124,7 @@ Every configurable undefined behavior has 3 possible modes:
 
 * `Compliant`: behaves as specified on a JVM
 * `Unchecked`: completely unchecked and undefined
-* `Fatal`: checked, but throws
-  [`UndefinedBehaviorError`s]({{ site.production_url }}/api/scalajs-library/{{ site.versions.scalaJS }}/#scala.scalajs.runtime.UndefinedBehaviorError)
-  instead of the specified exception.
+* `Fatal`: checked, but throws `UndefinedBehaviorError`s instead of the specified exception
 
 By default, undefined behaviors are in `Fatal` mode for `fastOptJS` and in
 `Unchecked` mode for `fullOptJS`.