fix(provisioning): make post-purge autoremove non-interactive

The `apt-get --purge autoremove` after the package removal pass had no
`-y`, so once removing modemmanager/wpasupplicant orphaned eleven
dependent packages, autoremove printed its "[Y/n] Abort." confirmation
and exited 1, aborting the run under errexit.

Add `-y` so the now-orphaned dependencies are purged without prompting,
consistent with the surrounding non-interactive apt invocations.

🤖 Generated with [Crush](https://github.com/charmassociates/crush)

Assisted-by: GLM-5 via Crush <crush@charm.land>

ProjectCode/SetupNewSystem.sh

@@ -115,7 +115,7 @@ function global-installPackages() {
     multipath-tools \
     || true
 
-    apt-get --purge autoremove
+    apt-get -y --purge autoremove
 
   # add stuff we want