[docs] Improve the Getting Started documentation content (mui#30808)

docs/src/pages/customization/how-to-customize/how-to-customize.md

@@ -177,10 +177,6 @@ const StyledSlider = styled(Slider, {
 
 {{"demo": "pages/customization/how-to-customize/DynamicCSSVariables.js"}}
 
-### Theme nesting
-
-{{"demo": "pages/customization/how-to-customize/DynamicThemeNesting.js"}}
-
 ## 4. Global theme variation
 
 In order to promote consistency between components, and manage the user interface appearance as a whole, MUI provides a mechanism to apply global changes.
@@ -225,7 +221,3 @@ If you are already using the [CssBaseline](/components/css-baseline/) component
    )
  }
 ```
-
-## 6. Custom class name
-
-Check out [ClassName Generator](/guides/classname-generator/) section for more details.

docs/src/pages/customization/theming/theming.md

@@ -160,30 +160,7 @@ theme = createTheme(theme, {
 });
 ```
 
-Think of creating a theme as a two-step composition process: first, you define the basic design options; then, you'll use these design options to compose other options (example above) or to override the design of specific components (example below).
-
-```js
-import { createTheme } from '@mui/material/styles';
-
-let theme = createTheme({
-  shape: {
-    borderRadius: 4,
-  },
-});
-
-theme = createTheme(theme, {
-  components: {
-    MuiChip: {
-      styleOverrides: {
-        root: {
-          // apply theme's border-radius instead of component's default
-          borderRadius: theme.shape.borderRadius,
-        },
-      },
-    },
-  },
-});
-```
+Think of creating a theme as a two-step composition process: first, you define the basic design options; then, you'll use these design options to compose other options.
 
 ### `responsiveFontSizes(theme, options) => theme`
 

docs/src/pages/getting-started/example-projects/example-projects.md

@@ -52,6 +52,7 @@ If you want to start with a more complete and real-world example, you could take
   - All PWA features included (SW, Notifications, deferred installation prompt and more)
   - Optimized and scalable performance (all ~100 points on Lighthouse)
 
+<!-- TODO: revert this once it is migrated to v5
 - [React SaaS Template](https://github.com/dunky11/react-saas-template):
 
   - ![stars](https://img.shields.io/github/stars/dunky11/react-saas-template.svg?style=social&label=Star)
@@ -60,23 +61,17 @@ If you want to start with a more complete and real-world example, you could take
   - Fully routed using react-router
   - Lazy loads components to boost performance
   - Components for statistics, text with emoji support, image upload and much more...
+-->
 
+<!-- TODO: revert this once it is migrated to v5
 - [Material Sense](https://github.com/alexanmtz/material-sense):
 
   - ![stars](https://img.shields.io/github/stars/alexanmtz/material-sense.svg?style=social&label=Star)
   - Graph using recharts
   - React Router included with a navigation example
   - A docker container with an Nginx server for production build
   - Created with Create React App
-
-- [RMUIF](https://github.com/rmuif/web):
-
-  - ![stars](https://img.shields.io/github/stars/rmuif/web.svg?style=social&label=Star)
-  - Bootstrapped with Create React App
-  - Firebase back-end with most of their products for the web included, e.g., Authentication and Cloud Firestore
-  - Routing with React Router, including protected routes and error handling
-  - Extensive and well-tested mobile support with full-screen dialogs and swipeable tabs
-  - Cross-platform application monitoring with Sentry
+-->
 
 ### Paid