chore(deps): Remove dependency on babel-eslint; simplify eslintrc f…

…or mocha tests (#5794)

* chore(deps): Remove deprecated babel-lint package

  When dependabot submitted PR #5791, it became apparent that eslint
  version >= 8 is incompatible with babel-eslint v10.1.0 despite the
  latter not having a version restriction against it.  This is probably
  because v10.1.0 is the last version of the package before it was
  deprecated and renamed @babel/eslint-parser.

  A little more investigation determined that there is no longer any
  need to have eslint use a non-default parser for tests/mocha/**/*.js,
  so the most straight forward solution is just to remove the dependency
  entirely.

* 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 #4062.

package.json

@@ -69,7 +69,6 @@
     "@blockly/dev-tools": "^2.6.1",
     "@blockly/theme-modern": "^2.1.1",
     "@wdio/selenium-standalone-service": "^7.10.1",
-    "babel-eslint": "^10.1.0",
     "chai": "^4.2.0",
     "clang-format": "^1.6.0",
     "closure-calculate-chunks": "^3.0.2",