display_url: Don't duplicate public_url and local_url if they are the same

[manics]

2.15.0 behaviour:

$ jupyter-server --ip=127.0.0.1

[I 2025-01-26 13:29:02.002 ServerApp] jupyter_server_terminals | extension was successfully linked.
[I 2025-01-26 13:29:02.026 ServerApp] jupyter_server_terminals | extension was successfully loaded.
[I 2025-01-26 13:29:02.030 ServerApp] Serving notebooks from local directory: /tmp/test
[I 2025-01-26 13:29:02.031 ServerApp] Jupyter Server 2.15.0 is running at:
[I 2025-01-26 13:29:02.031 ServerApp] http://127.0.0.1:8888/?token=TOKEN
[I 2025-01-26 13:29:02.031 ServerApp]     http://127.0.0.1:8888/?token=TOKEN
[I 2025-01-26 13:29:02.031 ServerApp] Use Control-C to stop this server and shut down all kernels (twice to skip confirmation).
[C 2025-01-26 13:29:02.034 ServerApp] 
    
    To access the server, open this file in a browser:
        file:///tmp/test/jpserver-1124142-open.html
    Or copy and paste one of these URLs:
        http://127.0.0.1:8888/?token=TOKEN
        http://127.0.0.1:8888/?token=TOKEN

With this PR:

$ jupyter-server --ip=127.0.0.1

[I 2025-01-26 13:30:09.408 ServerApp] jupyter_server_terminals | extension was successfully linked.
[I 2025-01-26 13:30:09.433 ServerApp] jupyter_server_terminals | extension was successfully loaded.
[I 2025-01-26 13:30:09.440 ServerApp] Serving notebooks from local directory: /tmp/test
[I 2025-01-26 13:30:09.440 ServerApp] Jupyter Server 2.16.0.dev0 is running at:
[I 2025-01-26 13:30:09.440 ServerApp] http://127.0.0.1:8888/?token=TOKEN
[I 2025-01-26 13:30:09.440 ServerApp] Use Control-C to stop this server and shut down all kernels (twice to skip confirmation).
[I 2025-01-26 13:30:09.440 ServerApp] Welcome to Project Jupyter! Explore the various tools available and their corresponding documentation. If you are interested in contributing to the platform, please visit the community resources section at https://jupyter.org/community.html.
[C 2025-01-26 13:30:09.444 ServerApp] 
    
    To access the server, open this file in a browser:
        file:///tmp/test/jpserver-1124538-open.html
    Or copy and paste one of these URLs:
        http://127.0.0.1:8888/?token=TOKEN