refactor(tests): Simplify tests/mocha/.eslintrc.json

Remove all rules that seem to be redundant with our top-level
.eslintrc.json.

This finishes reverting most of the changes made in PR google#4062.

tests/mocha/.eslintrc.json

@@ -10,30 +10,8 @@
     },
     "rules": {
         "no-unused-vars": ["off"],
-        "es5/no-arrow-functions": ["off"],
-        "es5/no-binary-and-octal-literals": ["off"],
-        "es5/no-block-scoping": ["off"],
-        "es5/no-classes": ["off"],
-        "es5/no-computed-properties": ["off"],
-        "es5/no-default-parameters": ["off"],
-        "es5/no-destructuring": ["off"],
-        "es5/no-es6-methods": ["off"],
-        "es5/no-es6-static-methods": ["off"],
-        "es5/no-for-of": ["off"],
-        "es5/no-generators": ["off"],
-        "es5/no-modules": ["off"],
-        "es5/no-object-super": ["off"],
-        "es5/no-rest-parameters": ["off"],
-        "es5/no-shorthand-properties": ["off"],
-        "es5/no-spread": ["off"],
-        "es5/no-template-literals": ["off"],
-        "es5/no-typeof-symbol": ["off"],
-        "es5/no-unicode-code-point-escape": ["off"],
-        "es5/no-unicode-regex": ["off"],
         // Allow uncommented helper functions in tests.
         "require-jsdoc": ["off"],
-        // In mocha tests in suites, `this` is meaningful and useful.
-        "no-invalid-this": ["off"],
         "prefer-rest-params": ["off"]
     },
     "extends": "../../.eslintrc.json"