Documentation sources contain outdated movedTo property

[julienrf]

Some sources of the Dotty website contain a movedTo property that was introduced when we were considering moving the source files to the scala/docs.scala-lang repo. Ultimately, we have followed a different approach and the source files in the Dotty are now the unique source of documentation. Therefore, we should remove the movedTo property from them.

[julienrf]

Maybe related to #15115 since we probably want to keep having a top banner, ultimately, but to indicate that this is the nightly documentation, with a link to find the stable documentation (what is currently at the URL movedTo…)