Fix error while updating the home page by admin

There is an error when we try to update the home page through admin panel:

```
Oops, you've missed a required field. Please complete before saving.
```

I happens, because the `posthogLabel` field was required for Liquidity Provider
Role section and it is not set by default in `stc/content/pages/index.md` file.
The posthog label for this button is not needed anyway so it was probably added
there by mistake.

static/admin/config.yml

@@ -355,11 +355,6 @@ collections:
                             },
                           ],
                       },
-                      {
-                        label: Posthog Label,
-                        name: posthogLabel,
-                        widget: string,
-                      },
                     ],
                 }
           - label: "Token Holder Role"