Remove the listener priorities configuration options

[ste93cry]

I know we discussed about removing these configuration options in the past, but I strongly believe that this kind of things should not be part of the bundle configuration mainly for these reasons:

• There is already a way to change this kind of things, which is writing a compiler pass or overriding the service
• I think that it's not a common thing to change this, in a lot of years of work with Symfony I rarely if never had to change the priority of a third-party listener
• Exposing this configuration to users puts it on an equal footing with changing any bundle or SDK option, which is false because it affects the inner workings of the bundle itself
• The listeners (for example the tracing listener I would like to implement in the near future) must run in a specific priority which correlates them. Letting users change such priorities will likely break things because they must know that they must also update all related priorities: at that point, you're falling into an advanced use-case which to me means that you also have the knowledge to implement the proper solution