rm doc/NEWS-update.jl step from CONTRIBUTING.md (#30482)

Update CONTRIBUTING.md to stop recommending that people run `./julia doc/NEWS-update.jl` after every `NEWS.md` change in every PR.

CONTRIBUTING.md

@@ -182,7 +182,7 @@ A doctest needs to match an interactive REPL including the `julia>` prompt. To r
 
 #### News-worthy changes
 
-For new functionality and other substantial changes, add a brief summary to `NEWS.md`. The news item should cross reference the pull request (PR) parenthetically, in the form `([#pr])`; after adding this, run `./julia doc/NEWS-update.jl` from the `julia` directory to update the cross-reference links. To add the PR reference number, first create the PR, then push an additional commit updating `NEWS.md` with the PR reference number.
+For new functionality and other substantial changes, add a brief summary to `NEWS.md`. The news item should cross reference the pull request (PR) parenthetically, in the form `([#pr])`. To add the PR reference number, first create the PR, then push an additional commit updating `NEWS.md` with the PR reference number. We periodically run `./julia doc/NEWS-update.jl` from the julia directory to update the cross-reference links, but this should not be done in a typical PR in order to avoid conflicting commits.
 
 #### Annotations for new features, deprecations and behavior changes