test: modernize mocha config (#581)

Author: JustinBeckwith

handwritten/datastore/.mocharc.json

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

handwritten/datastore/package.json

@@ -77,7 +77,6 @@
     "eslint-plugin-prettier": "^3.1.0",
     "google-proto-files": "^1.0.0",
     "gts": "^1.0.0",
-    "intelli-espower-loader": "^1.0.1",
     "jsdoc": "^3.6.2",
     "jsdoc-fresh": "^1.0.1",
     "jsdoc-region-tag": "^1.0.2",
@@ -86,7 +85,6 @@
     "mv": "^2.1.1",
     "ncp": "^2.0.0",
     "c8": "^7.0.0",
-    "power-assert": "^1.6.1",
     "prettier": "^1.17.1",
     "proxyquire": "^2.1.0",
     "sinon": "^8.0.0",