[HttpCache] removed x-debug-token from response metadata before storing it

| Q             | A
| ------------- | ---
| Bug fix?      | [yes]
| New feature?  | [no]
| BC breaks?    | [no]
| Deprecations? | [no]
| Tests pass?   | [yes]
| Fixed tickets | [#6227]
| License       | MIT

When using HttpCache on dev environment, looking up and finding a response satisfying the master request leads to a bug with the stopwatch component, because it tries to open a section that doesn't exists, the X-Debug-Token is from an older request.