Docs: remove outdated notes from migration guide (#10279)

docs/user-guide/migrating-to-5.0.0.md

@@ -91,8 +91,6 @@ For compatibility, ESLint v5 will treat `ecmaFeatures: { experimentalObjectRestS
 
 **To address:** If you use the `experimentalObjectRestSpread` option, you should be able to upgrade to ESLint v5 without any changes, but you will encounter a deprecation warning. To avoid the warning, use `ecmaVersion: 2018` in your config file rather than `ecmaFeatures: { experimentalObjectRestSpread: true }`. If you would like to disallow the use of other ES2018 features, consider using rules such as [`no-restricted-syntax`](/docs/rules/no-restricted-syntax).
 
-*Note: In the latest alpha release of ESLint v5, `experimentalObjectRestSpread` is not yet implemented as an alias for `ecmaVersion: 2018`, so configs that use `experimentalObjectRestSpread` may temporarily cause parsing errors. We plan to add this alias in a future prerelease.*
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 ## <a name="nonexistent-files"></a> Linting nonexistent files from the command line is now a fatal error
 
 Previous versions of ESLint silently ignored any nonexistent files and globs provided on the command line:
@@ -114,8 +112,6 @@ Note that this also affects the [`CLIEngine.executeOnFiles()`](https://eslint.or
 
 If you use a boilerplate generator that relies on this behavior (e.g. to generate a script that runs `eslint tests/` in a new project before any test files are actually present), you can work around this issue by adding a dummy file that matches the given pattern (e.g. an empty `tests/index.js` file).
 
-*Note: This change has not yet appeared in the latest alpha release. We plan to add it in a future prerelease.*
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 ## <a name="deprecated-globals"></a> Deprecated globals have been removed from the `node`, `browser`, and `jest` environments
 
 Some global variables have been deprecated or removed for code running in Node.js, browsers, and Jest. (For example, browsers used to expose an `SVGAltGlyphElement` global variable to JavaScript code, but this global has been removed from web standards and is no longer present in browsers.) As a result, we have removed these globals from the corresponding `eslint` environments, so use of these globals will trigger an error when using rules such as [`no-undef`](/docs/rules/no-undef).