Remove Vue ESLint plugin for Vite compatibility

The Vue ESLint plugin is not compatible with Vite and isn't provided in
Vite's default template. By removing it, the codebase progresses toward
the migration to Vue 3.0 and Vite (#230).

Changes:

- Directly execute `eslint` in the `npm run lint:eslint` command.
- Fix previously undetected linting issues that weren't covered by Vue
  CLI's default configuration.
- Updated various configuration files, reflecting the removal and lint
  fixes.
- Remove unused `eslint-plugin-import` dependency that is already
  imported by `@vue/eslint-config-airbnb-with-typescript`.

In `.eslintrc.cjs`:

- Add `es2022` as environment in to simplify setting parser options and
  align with Vite starter configuration.
- Remove useless tests override.
- Move tests override in root `.eslintrc.cjs` to `tests/` for clarity,
  better organization, scalability and separation of concerns.

.eslintrc.cjs

@@ -6,6 +6,7 @@ module.exports = {
   root: true,
   env: {
     node: true,
+    es2022: true, // add globals and sets parserOptions.ecmaVersion to 2022
   },
   extends: [
     // Vue specific rules, eslint-plugin-vue
@@ -20,36 +21,12 @@ module.exports = {
     // Added by Vue CLI
     '@vue/typescript/recommended',
   ],
-  parserOptions: {
-    ecmaVersion: 2022, // So it allows top-level awaits
-    /*
-      Having 'latest' leads to:
-      ```
-        Parsing error: ecmaVersion must be a number. Received value of type string instead
-      ```
-      For .js files in the project
-    */
-  },
   rules: {
     ...getOwnRules(),
     ...getTurnedOffBrokenRules(),
     ...getOpinionatedRuleOverrides(),
     ...getTodoRules(),
   },
-  overrides: [
-    {
-      files: [
-        '**/__tests__/*.{j,t}s?(x)',
-        '**/tests/unit/**/*.spec.{j,t}s?(x)',
-      ],
-    },
-    {
-      files: ['**/tests/**/*.{j,t}s?(x)'],
-      rules: {
-        'no-console': 'off',
-      },
-    },
-  ],
 };
 
 function getOwnRules() {