[SMRT] Fix warnings in VRFCoordinatorV2Mock (and all solidity warnings)

Description
Fix warnings in VRFCoordinatorV2Mock.

Warnings are critical for developers to pay attention to, so cluttering up the solidity compiler output creates headaches for devs. Please fix these warnings. (Most of them are "unused parameter", so either use the parameter or comment them out)

(Note, chainlink-brownie-contracts is a minimal package that includes just the contracts of @chainlink/contracts, so it's quicker and smaller to download)

warning[5667]: Warning: Unused function parameter. Remove or comment out the variable name to silence this warning.
   --> lib/chainlink-brownie-contracts/contracts/src/v0.8/mocks/VRFCoordinatorV2Mock.sol:306:45:
    |
306 |   function requestSubscriptionOwnerTransfer(uint64 _subId, address _newOwner) external pure override {
    |                                             ^^^^^^^^^^^^^



warning[5667]: Warning: Unused function parameter. Remove or comment out the variable name to silence this warning.
   --> lib/chainlink-brownie-contracts/contracts/src/v0.8/mocks/VRFCoordinatorV2Mock.sol:306:60:
    |
306 |   function requestSubscriptionOwnerTransfer(uint64 _subId, address _newOwner) external pure override {
    |                                                            ^^^^^^^^^^^^^^^^^



warning[5667]: Warning: Unused function parameter. Remove or comment out the variable name to silence this warning.
   --> lib/chainlink-brownie-contracts/contracts/src/v0.8/mocks/VRFCoordinatorV2Mock.sol:310:44:
    |
310 |   function acceptSubscriptionOwnerTransfer(uint64 _subId) external pure override {
    |                                            ^^^^^^^^^^^^^



warning[5667]: Warning: Unused function parameter. Remove or comment out the variable name to silence this warning.
   --> lib/chainlink-brownie-contracts/contracts/src/v0.8/mocks/VRFCoordinatorV2Mock.sol:314:33:
    |
314 |   function pendingRequestExists(uint64 subId) public view override returns (bool) {
    |                                 ^^^^^^^^^^^^



warning[2018]: Warning: Function state mutability can be restricted to pure
   --> lib/chainlink-brownie-contracts/contracts/src/v0.8/mocks/VRFCoordinatorV2Mock.sol:261:3:
    |
261 |   function getConfig()
    |   ^ (Relevant source part starts here and spans across multiple lines).



warning[2018]: Warning: Function state mutability can be restricted to pure
   --> lib/chainlink-brownie-contracts/contracts/src/v0.8/mocks/VRFCoordinatorV2Mock.sol:274:3:
    |
274 |   function getFeeConfig()
    |   ^ (Relevant source part starts here and spans across multiple lines).



warning[2018]: Warning: Function state mutability can be restricted to pure
   --> lib/chainlink-brownie-contracts/contracts/src/v0.8/mocks/VRFCoordinatorV2Mock.sol:302:3:
    |
302 |   function getFallbackWeiPerUnitLink() external view returns (int256) {
    |   ^ (Relevant source part starts here and spans across multiple lines).



warning[2018]: Warning: Function state mutability can be restricted to pure
   --> lib/chainlink-brownie-contracts/contracts/src/v0.8/mocks/VRFCoordinatorV2Mock.sol:314:3:
    |
314 |   function pendingRequestExists(uint64 subId) public view override returns (bool) {
    |   ^ (Relevant source part starts here and spans across multiple lines).

Start with lib/chainlink-brownie-contracts/contracts/src/v0.8/mocks/VRFCoordinatorV2Mock.sol and inspect the functions at the warning locations in the issue. Run the Solidity compiler to confirm the reported warnings, then verify that the mock and other Solidity contracts produce no warnings.