Remove JAX from pip install in Job Search III lecture

The JAX library is already included in the base environment and doesn't need
to be explicitly installed, which was causing build failures.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: jstac

lectures/mccall_model_with_sep_markov.md

@@ -49,7 +49,7 @@ libraries
 ```{code-cell} ipython3
 :tags: [hide-output]
 
-!pip install quantecon jax
+!pip install quantecon
 ```
 
 We use the following imports: