hardcoded Genesis validator root

[Redidacove]

What does this PR do? Why is it needed ?
Replaced hardcoded value everywhere where fn was called to compute it from state calling st.GenesisValidatorRoot()
Which issues(s) does this PR fix ?
Fixes
Issue #14364

Other notes for review
Currently just replaced hardcoded value in
Rpc package
slasher package
P2p package
If asked can also do that for sync

[Redidacove]

@nisdas Just asking if I can include sync package changes as well in this one or should I be opening it in future Pr

[nisdas]

Lets do the rpc package first here

[james-prysm]

There are definitely more places that are needlessly pulling genesis validators root that should probably be updated, not sure if it should be in this PR or separately i.e.

prysm/validator/accounts/wallet/wallet.go

Line 359 in df4ca54

if !bytesutil.IsValidRoot(config.GenesisValidatorsRoot) {

[Redidacove]

There are definitely more places that are needlessly pulling genesis validators root that should probably be updated, not sure if it should be in this PR or separately i.e.

prysm/validator/accounts/wallet/wallet.go

Line 359 in df4ca54

if !bytesutil.IsValidRoot(config.GenesisValidatorsRoot) {

I was asked to do for rpc only for now so removed those changes and that's why closed previous pr which had much more changes including yours and sync package and others.

[Redidacove]

@nisdas srry for lint fails, fixed it now

[nisdas]

FAIL: TestNodeServer_GetGenesis (0.06s)
FAIL: TestWaitForChainStart_AlreadyStarted (0.00s)

These 2 tests fail now along with our E2E tests