test: modernize mocha config (googleapis#610)

Author: JustinBeckwith

handwritten/bigtable/.mocharc.json

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

handwritten/bigtable/package.json

@@ -86,7 +86,6 @@
     "eslint-plugin-node": "^11.0.0",
     "eslint-plugin-prettier": "^3.0.0",
     "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",
@@ -97,11 +96,9 @@
     "npc": "0.0.1",
     "c8": "^7.0.0",
     "p-queue": "^6.0.2",
-    "power-assert": "^1.4.4",
     "prettier": "^1.7.4",
     "proxyquire": "^2.0.0",
     "sinon": "^8.0.0",
-    "source-map-support": "^0.5.10",
     "typescript": "3.6.4",
     "uuid": "^3.0.1"
   },