Remove dead code (unreferenced client) in `src/main/java/redis/clients/jedis/JedisPubSubBase` module.

[50-Course]

There is a commented code meant to initially invalidate client connection when the Connection is no longer listening. However, it is currently being bypassed, and does not actually reference anything in the JVM.

This patch aims to remove it - therefore, and as such does not introduces breaking change to the actual module.