Remove obsolete code

[shamil-gadelshin]

Description

This PR cleans obsolete code related to aggregated staking extrinsics.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Other (please describe): clean-up

Checklist

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have run cargo fmt and cargo clippy to ensure my code is formatted and linted correctly
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[l0r1s]

Maybe we need to try re-run e2e tests

[ales-otf]

Maybe we need to try re-run e2e tests

hmm triggered re-run, but it failed again