developer-guide: Clean up host dependencies

pzstd is now provided via subtool when initializing the SDK.

xz is no longer used, as the SDK compression format was changed to
zstd.

BUG=b:357472594
TEST=CQ

Change-Id: Ibae97465525845e1f930375da919cf8dc8d5ac3e
Reviewed-on: https://chromium-review.googlesource.com/c/website/+/5838864
Reviewed-by: Tim Bain <tbain@google.com>
Commit-Queue: Jack Rosenthal <jrosenth@chromium.org>
diff --git a/site/chromium-os/developer-library/guides/development/developer-guide/index.md b/site/chromium-os/developer-library/guides/development/developer-guide/index.md
index 2f7f3bf..907378d 100644
--- a/site/chromium-os/developer-library/guides/development/developer-guide/index.md
+++ b/site/chromium-os/developer-library/guides/development/developer-guide/index.md
@@ -186,7 +186,7 @@
 (outside)
 # On Ubuntu, make sure to enable the universe repository.
 $ sudo add-apt-repository universe
-$ sudo apt-get install git gitk git-gui curl xz-utils zstd
+$ sudo apt-get install git gitk git-gui curl
 ```
 
 These commands also installs git's graphical front end (`git gui`) and revision