Remove userBlock event attribute key prefix

[RiccardoM]

Bug description

Looking at this transaction, we can see that the block_user event has the following attributes:

{
  "type": "block_user",
  "attributes": [
    {
      "key": "userBlock_blocker",
      "value": "desmos16t82uc3cs0tszpcx363rwk8yx6dthcyrjcn9d4"
    },
    {
      "key": "userBlock_blocked",
      "value": "desmos1uj9c9929scde78wu3u5r99wcavf2fzl7rdesmh"
    },
    {
      "key": "subspace",
      "value": "4e188d9c17150037d5199bbdb91ae1eb2a78a15aca04cb35530cccb81494b36e"
    },
    {
      "key": "userBlock_reason",
      "value": "You have a lot of stake"
    }
  ]
}

As we can see, some keys have the prefix of userBlock_. We can remove this.