Remove deprecations for the v0.4.0 release

There is only one deprecation for this release:

The **Solr Operator Helm chart** option:

```yaml
useZkOperator: "true"
```

has been replaced by:

```yaml
zookeeper-operator:
  use: true
```

Note: The new option is a `boolean` value, while the deprecated option is a `string` value.