fix: Translate "None" option in agent assignment dropdown (#11060)

# Pull Request Template

## Description

This PR includes a translation update for the "None" option in the agent
assignment multi-select dropdown.

Fixes
https://linear.app/chatwoot/issue/CW-4140/none-option-in-assign-agent-multi-select-is-not-translated

## Type of change

- [x] Bug fix (non-breaking change which fixes an issue)

## How Has This Been Tested?

**Test cases**
1. Check in conversation sidebar
2. Check in command bar
3. Check in participation dropdown


## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [x] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

app/javascript/dashboard/helper/agentHelper.js

@@ -1,16 +1,3 @@
-/**
- * Default agent object representing 'None'
- * @type {Object}
- */
-export const createNoneAgent = {
-  confirmed: true,
-  name: 'None',
-  id: 0,
-  role: 'agent',
-  account_id: 0,
-  email: 'None',
-};
-
 /**
  * Filters and sorts agents by availability status
  * @param {Array} agents - List of agents
@@ -62,22 +49,3 @@ export const getAgentsByUpdatedPresence = (
   );
   return agentsWithDynamicPresenceUpdate;
 };
-
-/**
- * Combines the filtered agents with the 'None' agent option if applicable.
- *
- * @param {Array} filteredAgentsByAvailability - The list of agents sorted by availability.
- * @param {boolean} includeNoneAgent - Whether to include the 'None' agent option.
- * @param {boolean} isAgentSelected - Whether an agent is currently selected.
- * @returns {Array} The combined list of agents, potentially including the 'None' agent.
- */
-export const getCombinedAgents = (
-  filteredAgentsByAvailability,
-  includeNoneAgent,
-  isAgentSelected
-) => {
-  return [
-    ...(includeNoneAgent && isAgentSelected ? [createNoneAgent] : []),
-    ...filteredAgentsByAvailability,
-  ];
-};