test: modernize mocha config (#720)

Author: JustinBeckwith

packages/packages/google-gax/.mocharc.json

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

packages/packages/google-gax/package.json

@@ -44,7 +44,6 @@
     "@types/rimraf": "^2.0.2",
     "@types/semver": "^6.0.0",
     "@types/sinon": "^7.0.0",
-    "@types/source-map-support": "^0.5.0",
     "@types/through2": "^2.0.33",
     "c8": "^7.0.0",
     "chai": "*",
@@ -59,7 +58,6 @@
     "fs-extra": "^8.0.0",
     "google-proto-files": "^1.0.0",
     "gts": "^1.0.0",
-    "intelli-espower-loader": "^1.0.1",
     "is-docker": "^2.0.0",
     "json-loader": "^0.5.7",
     "karma": "^4.1.0",
@@ -82,7 +80,6 @@
     "puppeteer": "^2.0.0",
     "rimraf": "^3.0.0",
     "sinon": "^8.0.0",
-    "source-map-support": "^0.5.6",
     "stream-events": "^1.0.4",
     "through2": "^3.0.0",
     "ts-loader": "^6.0.3",