Solana chain-capability: proto removed upstream, generated code orphaned

[nadahalli]

The Solana blockchain proto (capabilities/blockchain/solana/v1alpha/client.proto) was removed from chainlink-protos in smartcontractkit/chainlink-protos#300, but the generated Go code in pkg/capabilities/v2/chain-capabilities/solana/ is still here and still imported by chainlink core (core/capabilities/remote/executable/hasher.go).

The generate.go that referenced the removed proto has been deleted in #1903 to unbreak make generate. The generated code compiles fine without the proto, but it can never be regenerated.

This needs a decision:

1. Restore the proto in chainlink-protos if solana chain capabilities are still needed
2. Remove the generated code from chainlink-common and the import from chainlink core's hasher.go if they're not

Current state (proto gone, generated code orphaned, generate.go deleted as workaround) should be cleaned up.