In the past when Undertow was supporting also JDK 8 we
used to use Jetty ALPN provider [1] on IBM JDK8.
This has changed with modular JDKs starting from JDK 9 see [2]
Modular JDKs come with their own ALPN providers.
Since we don't support JDK8 anymore it is safe to remove Jetty ALPN provider.

[1] https://webtide.com/jetty-alpn-java-8u252/
[2] https://www.ibm.com/docs/en/was-liberty/base?topic=40-alpn-support