docs: fix remaining "Embedded FrankenPHP" framing in embed.md

The binary produced by the embed feature contains FrankenPHP plus the
user's PHP application; FrankenPHP itself is not what is being
embedded. Drop the misleading "FrankenPHP" qualifier from
`## Using the Embedded Binary` so it is consistent with the surrounding
headings (`## PHP Extensions in the Embedded Binary`,
`## Customizing the Embedded Binary Build`, `## Distributing the
Embedded Binary`).

Author: dunglas

docs/embed.md

@@ -103,7 +103,7 @@ EMBED=/path/to/your/app ./build-static.sh
 
 The resulting binary is the file named `frankenphp-<os>-<arch>` in the `dist/` directory.
 
-## Using the Embedded FrankenPHP Binary
+## Using the Embedded Binary
 
 This is it! The `my-app` file (or `dist/frankenphp-<os>-<arch>` on other OSes) contains your self-contained app!