remove unstable docs

Author: GuillaumeGomez

src/doc/rustdoc/src/command-line-arguments.md

@@ -371,7 +371,7 @@ $ rustdoc src/lib.rs --themes /path/to/your/theme/file.css
 Note that the theme's name will be the file name without its extension. So if you pass
 `/path/to/your/theme/file.css` as theme, then the theme's name will be `file`.
 
-### `check-theme`: check if your themes implement all the required rules
+### `check-themes`: check if your themes implement all the required rules
 
 This flag allows you to check if your themes implement the necessary CSS rules. To put it more
 simply, when adding a new theme, it needs to implements all the CSS rules present in the "light"
@@ -380,5 +380,5 @@ CSS theme.
 You can use this flag like this:
 
 ```bash
-$ rustdoc --check-theme /path/to/your/theme/file.css
+$ rustdoc --check-themes /path/to/your/theme/file.css
 ```

src/doc/rustdoc/src/unstable-features.md

@@ -294,30 +294,6 @@ some consideration for their stability, and names that end in a number). Giving
 `rustdoc` will disable this sorting and instead make it print the items in the order they appear in
 the source.
 
-### `--themes`: provide additional themes
-
-Using this flag looks like this:
-
-```bash
-$ rustdoc src/lib.rs -Z unstable-options --themes theme.css
-```
-
-Giving this flag to `rustdoc` will make it copy your theme into the generated crate docs and enable
-it in the theme selector. Note that `rustdoc` will reject your theme file if it doesn't style
-everything the "light" theme does. See `--check-theme` below for details.
-
-### `--check-theme`: verify theme CSS for validity
-
-Using this flag looks like this:
-
-```bash
-$ rustdoc -Z unstable-options --check-theme theme.css
-```
-
-Before including your theme in crate docs, `rustdoc` will compare all the CSS rules it contains
-against the "light" theme included by default. Using this flag will allow you to see which rules are
-missing if `rustdoc` rejects your theme.
-
 ### `--resource-suffix`: modifying the name of CSS/JavaScript in crate docs
 
 Using this flag looks like this: