Reinstate commitment param on getSignatureStatuses to support old clients

[CriesofCarrots]

Problem

Using an old client/cli with the new rpc results in commitment-related errors:

$ solana airdrop 10 --url http://devnet.solana.com

Requesting airdrop of 10 SOL from 35.233.193.70:9900
Error: rpc request error: RPC Error response: {"code":-32602,"message":"Invalid params: missing field searchTransactionHistory."}

Summary of Changes

• Reinstate commitment to support old clients, mark as deprecated to be removed on next client release

[mvines]

How about we just land this on 1.1 and 1.0, not master. No need to remove the deprecated code then, it just disappears

[CriesofCarrots]

How about we just land this on 1.1 and 1.0, not master. No need to remove the deprecated code then, it just disappears

Ah, good idea. Will do!