fix(ct): remove yargs as unused dep

Removes yargs as a dependency from the contracts package since it wasn't
being used. Always good to cut unused dependencies.

.changeset/khaki-chefs-call.md

+---
+'@eth-optimism/contracts': patch
+---
+
+Remove yargs as a contracts dependency (unused)

packages/contracts/.depcheckrc

@@ -6,5 +6,4 @@ ignores: [
   "prettier-plugin-solidity",
   "solhint-plugin-prettier",
   "ts-generator",
-  "yargs",
 ]

packages/contracts/package.json

@@ -119,8 +119,7 @@
     "ts-generator": "0.0.8",
     "ts-node": "^10.0.0",
     "typechain": "^6.0.2",
-    "typescript": "^4.3.5",
-    "yargs": "^16.2.0"
+    "typescript": "^4.3.5"
   },
   "peerDependencies": {
     "ethers": "^5"