Remove a check for a valid nonce and mutex from StakerProxy.stake()

[pgev]

• Remove a check for a valid nonce from StakerProxy.stake()

In the context of OSTComposer functionality, we've already checked the validity of a provided nonce within OSTComposer::requestStake() function (to make sure that OSTComposer::acceptStakeRequest() would not fail because of an invalid nonce).

In the context of StakerProxy::stake() function this check is not needed as a call to gateway stack function would assure this.

• Replace StakerProxy's own implementation of a mutex by inheriting from Mutex contract.
• Remove mutex from OSTComposer::acceptStakeRequest function.

We can safely remove a mutex from OSTComposer::acceptStakeRequest and execute the following statements after the first require statement in the function:

delete stakeRequestHashes[stakeRequest.staker][address(stakeRequest.gateway)];
delete stakeRequests[_stakeRequestHash];

• Remove mutex from OSTComposer::revokeStakeRequest and OSTComposer::rejectStakeRequest

We can safely remove mutex from OSTComposer::revokeStakeRequest and OSTComposer::rejectStakeRequest as the following statements in function OSTComposer::removeStakeRequest (called within above-mentioned functions) protects against reentrancy:

        delete stakeRequestHashes[staker][address(stakeRequest.gateway)];
        delete stakeRequests[_stakeRequestHash];

[abhayks1]

Started working on it 🚗