Clear epoch values for root subnets.

[shamil-gadelshin]

Description

This PR removes values for root subnets from the following storage item list:

• SubnetworkN
• Tempo
• ActivityCutoff
• Bonds
• Keys
• MaxAllowedValidators
• SubnetOwnerHotkey
• Kappa
• BondsPenalty
• Yuma3On
• BlockAtRegistration
• Rank
• Trust
• Active
• Emission
• Consensus
• Incentive
• Dividends
• LastUpdate
• PruningScores
• ValidatorTrust
• ValidatorPermit
• StakeWeight

Related Issue(s)

• Closes https://github.com/opentensor/subtensor/issues/939

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):

Checklist

• [x] I have performed a self-review of my own code
• [ ] I have commented my code, particularly in hard-to-understand areas
• [x] 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
• [x] My changes generate no new warnings
• [x] 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

[shamil-gadelshin]

Merge after this PR: https://github.com/opentensor/subtensor/pull/1700