Feature Request: Add remove node admin message

**Proposed Implementation:**
When executed with a node number, the `--remove-node` command would send the remove_by_nodenum admin message to the device's radio firmware. This would remove the specified node from the nodedb.

Example:
```
meshtastic --remove-node 12345
```

**Benefits:**
- Allows managing the nodedb from the CLI
- Consistent with other clients