Remove `pybamm_install_jax` and references to it

[agriyakhetarpal]

Based on https://github.com/pybamm-team/PyBaMM/issues/4127#issuecomment-2145762187 and pointed out by @DavidMStraub, after v24.5 gets released on PyPI, the pybamm_install_jax entry point and its corresponding method install_jax in pybamm/util.py can be removed from the source code for v24.9, following the completion of its deprecation cycle since v23.9.

There might be a few references in the documentation about it as well, I have not checked those at this time.