As a tool developer I want to be able to remove old or wrong information in a given language on a item's label
DELETE /entities/items/{item_id}/labels/{lang_code}
**Acceptance criteria:**
- On the successful removal, API should respond with 200 and "label deleted" as a response body.
- 200 response should also contain Content-Language header with "en" as a value
- Following error cases have to be considered:
<table>
<tr>
<th>
</th>
<th>HTTP response code</th>
<th>response payload</th>
</tr>
<tr>
<td>Item does not exist</td>
<td>404</td>
<td>
`"code": "item-not-found"`
`"message": "Could not find an item with the ID: {item_id}"`
</td>
</tr>
<tr>
<td>Invalid item ID</td>
<td>400</td>
<td>
`"code": "invalid-item-id"`
`"message": "Not a valid item ID: <ITEM_ID>"`
</td>
</tr>
<tr>
<td>Invalid language code</td>
<td>400</td>
<td>
`"code": "invalid-language-code"`
`"message": "Not a valid language code : <language code>"`
</td>
</tr>
<tr>
<td>Item does not have label in given language</td>
<td>404</td>
<td>
`"code": "label-not-defined"`
`"message": "Item with the ID <ITEM_ID> does not have a label in the language: <LANGUAGE CODE>"`
</td>
</tr>
<tr>
<td>Invalid edit tag</td>
<td>400</td>
<td>
`{ "code": "invalid-edit-tag", "message": "Invalid MediaWiki tag: {tag}" }`
</td>
</tr>
<tr>
<td>Comment too long</td>
<td>400</td>
<td>
`{"code": "comment-too-long", "message": "Comment must not be longer than {limit} characters"}`
</td>
</tr>
</table>
**Notes:**
- "Automated edit summary" related to the edit to be of form: /* wbsetlabel-remove:1| */ "
- client can provide additional edit metadata: mediawiki tags, edit summary text to append to the automated summary, and a bot edit flag, like in DELETE /entities/items/{item_id}/statements/{statement_id}
- Allow empty request body.
- Handle HTTP conditional request headers as in DELETE /entities/item/{item_id}/statements/{statement_id} (DOUBLE CHECK)
- Handle user authentication/authorization like in DELETE /entities/items/{item_id}/statements/{statement_id}