Clean slot_sources_proxy dependencies

Problem/Motivation

Before tagging beta1, without going as far as #3529494: Remove SlotSourceProxy, we can tidy slot_sources_proxy dependencies:

  display_builder.slot_sources_proxy:
    class: Drupal\display_builder\SlotSourceProxy
    arguments:
      - '@plugin.manager.ui_patterns_source'
      - '@entity.memory_cache'
      - '@plugin.manager.ui_patterns_source'
      - '@entity.memory_cache'

They have duplicate valeus (maybe a rebase error) and the service doesn't need memory_cache anymore:

  public function __construct(
    protected PluginManagerInterface $sourceManager,
  ) {}

Proposed resolution

Remove dependencies.