docs(packages): drop removed Zsh 5.1.1/5.2.4 from version list

The zsh package no longer ships 5.1.1 or 5.2.4 as selectable profiles
(z-shell/zsh#14). Remove the two stale 'zi pack' examples so the usage page
matches the available manifest profiles.

Author: ss-o

ecosystem/packages/02_usage.mdx

@@ -893,8 +893,6 @@ zi pack"5.6.2" for zsh
 zi pack"5.5.1" for zsh
 zi pack"5.4.2" for zsh
 zi pack"5.3.1" for zsh
-zi pack"5.2.4" for zsh
-zi pack"5.1.1" for zsh
 ```
 
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