Remove unused migration.

[FiberMan]

• remove hardcoded storage versions
• remove migrations call from the hooks since it's not used
• fix signal pallet tests

Test scenario:

• build --release ok
• build --benchmarks ok
• make test ok

[vovacha]

I'm not a big fan of having commented code in the repo.
Could you uncomment it and leave it as a template? So all future migrations will use this approach with the StorageVersion trait.

[FiberMan]

I'm not a big fan of having commented code in the repo. Could you uncomment it and leave it as a template? So all future migrations will use this approach with the StorageVersion trait.

Tbh, I'm not a fan of having some code in repo that is not in use :)
We can restore it from GIT history if needed.
Removing unused files.

[vayesy]

I can see we would still have issues with future migrations, which can be applied multiple times. Shouldn't this PR implement a solution for that by storing pallet version in the storage and deciding on migrations based on that value?

[FiberMan]

StorageVersion defaults to 0 when it is not present in the storage.
So on the next migration, we will need something like this:

1. get on-chain storage version.
2. apply migration which version is next to the one on chain.
3. update on-chain storage version.

[vovacha]

I can see we would still have issues with future migrations, which can be applied multiple times. Shouldn't this PR implement a solution for that by storing pallet version in the storage and deciding on migrations based on that value?

As far as I understand it's a global storage, not a pallet storage and it works like this:

use frame_support::traits::{GetStorageVersion, StorageVersion}

## Get Pallet's storage version
let on_chain_storage_version = <P as GetStorageVersion>::on_chain_storage_version();

## Do migrations
...

## Set the new pallet's storage version
StorageVersion::new(4).put::<P as GetStorageVersion>();

[vovacha]

@FiberMan please, change the target branch from main to release.