Remove addition of label during context init

[RLKRo]

Description

During context init start_label is added to ctx.labels if ctx.requests is empty. The same does not happen when using pipeline (after the first request is added, there are no labels during actor execution).

This can lead to ctx.label having more items than ctx.requests or ctx.responses at the end of each turn.

Checklist

• I have covered the code with tests
• I have added comments to my code to help others understand it
• I have updated the documentation to reflect the changes
• I have performed a self-review of the changes