[FEATURE] Remove Update Batch Size

### Please describe the purpose of the feature. Is it related to a problem?
This is somewhere between a feature and maintenance. Having to vmap an extra time is not necessarily as good an idea as we thought when we started rewriting Mava in JAX. I think it would be better to rather be able to use twice as many environments and then only have an outer `pmap`. It'll also remove a non-standard config option.

### Describe the solution you'd like
Remove the update_batch_size config option and update all systems accordingly.

### How do we know when implementation of this feature is complete?
Checklist:
- [ ] All systems are benchmarked and can get similar performance.

Start by locating the update_batch_size configuration and its references across the systems in the Mava repository. Review how the current vmap and outer pmap flow is assembled, then benchmark every affected system. Done means the option is removed, all systems are updated, and benchmarks show similar performance.

Written by the indexing model from the issue text.