test: modernize mocha config (#202)

Author: JustinBeckwith

packages/google-cloud-securitycenter/.mocharc.json

@@ -0,0 +1,5 @@
+{
+  "enable-source-maps": true,
+  "throw-deprecation": true,
+  "timeout": 10000
+}

packages/google-cloud-securitycenter/package.json

@@ -46,14 +46,12 @@
     "eslint-config-prettier": "^6.0.0",
     "eslint-plugin-node": "^11.0.0",
     "eslint-plugin-prettier": "^3.0.0",
-    "intelli-espower-loader": "^1.0.1",
     "jsdoc": "^3.6.2",
     "jsdoc-fresh": "^1.0.1",
     "jsdoc-region-tag": "^1.0.2",
     "linkinator": "^1.5.0",
     "mocha": "^7.0.0",
     "c8": "^7.0.0",
-    "power-assert": "^1.4.4",
     "prettier": "^1.7.4"
   }
 }