As of #9596, task-runner is no longer used.
Due to how the build system works, task-runner was providing nim-stew,
nim-bearssl and nim-chronos to the project, even though these are also
top-level dependencies - effectively this means there were multiple
versions of these libraries in the source tree and it is not entirely
intuitive which is actually used - adding to the confusion, the
submodule was pinning different versions.
This PR removes task-runner and resets the other dependencies to the
versions in task-runner thus minimising collateral changes.
A duplicate copy of bearssl is also removed.
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