build: delete legacy ESLint config and obsolete helpers

Remove legacy ESLint configuration files that are superseded by
`eslint.config.cjs` (flat config):

Deleted files:
- `.eslintrc.js` (root entry point)
- `.eslintignore` (ignores are in flat config)
- `etc/eslint/.eslintrc.overrides.js`
- `etc/eslint/.eslintrc.benchmarks.js`
- `etc/eslint/.eslintrc.examples.js`
- `etc/eslint/.eslintrc.tests.js`
- `etc/eslint/overrides/index.js`
- `etc/eslint/overrides/repl_namespace.js`

Updated files:
- `eslint.config.cjs`: inline restricted syntax config (was imported
  from the now-deleted overrides module); remove overrides import
- `etc/eslint/.eslintrc.js`: remove overrides import (kept for now
  as `typescript.js` depends on it for base rule definitions)

Kept for now:
- `etc/eslint/.eslintrc.js` (consumed by `typescript.js`)
- `etc/eslint/.eslintrc.typescript.js` (consumed by remark plugin)
- `etc/eslint/.eslintrc.typescript.tests.js`
- `etc/eslint/.eslintrc.markdown.js` (consumed by remark plugin)
- `etc/eslint/env/`, `parser-options/`, `plugins/`, `rules/`

Ref: stdlib-js/metr-issue-tracker#54

Author: Planeshifter

.eslintignore

@@ -33,12 +33,24 @@ var pluginExpectType = require( 'eslint-plugin-expect-type' );
 var stdlibPlugin = require( './lib/node_modules/@stdlib/_tools/eslint/rules/scripts/plugin.js' );
 var allRules = require( './etc/eslint/rules' );
 var tsRules = require( './etc/eslint/rules/typescript.js' );
-var overrides = require( './etc/eslint/overrides' );
 
 
 // VARIABLES //
 
-var restrictedSyntaxConfig = overrides[ 1 ].rules[ 'no-restricted-syntax' ];
+var restrictedSyntaxConfig = [ 'error',
+	'ArrowFunctionExpression', 'ClassBody', 'ClassDeclaration',
+	'ClassExpression', 'DebuggerStatement', 'ExperimentalRestProperty',
+	'ExperimentalSpreadProperty', 'LabeledStatement', 'RestElement',
+	'SpreadElement', 'TaggedTemplateExpression', 'TemplateElement',
+	'TemplateLiteral', 'WithStatement', 'YieldExpression',
+	'JSXIdentifier', 'JSXNamespacedName', 'JSXMemberExpression',
+	'JSXEmptyExpression', 'JSXExpressionContainer', 'JSXElement',
+	'JSXClosingElement', 'JSXOpeningElement', 'JSXAttribute',
+	'JSXSpreadAttribute', 'JSXText', 'ExportDefaultDeclaration',
+	'ExportNamedDeclaration', 'ExportAllDeclaration', 'ExportSpecifier',
+	'ImportDeclaration', 'ImportSpecifier', 'ImportDefaultSpecifier',
+	'ImportNamespaceSpecifier'
+];
 var nonClonableRules = {};
 var rules = {};
 var val;

.eslintrc.js

@@ -55,15 +55,6 @@ eslint.env = require( './env' );
 */
 eslint.rules = require( './rules' );
 
-/**
-* Overrides.
-*
-* @name overrides
-* @memberof eslint
-* @type {Array}
-*/
-eslint.overrides = require( './overrides/repl_namespace.js' );
-
 /**
 * Parser options.
 *