engine: install: remove Ubuntu 20.04, Fedora 40 (EOL) (#22675)

Ubuntu 20.04 and Fedora 40 reached EOL, so remove mentions of it in the
installation docs.

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## Description

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## Related issues or tickets

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- [ ] Technical review
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---------

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

content/manuals/desktop/setup/install/linux/fedora.md

@@ -25,7 +25,7 @@ This page contains information on how to install, launch and upgrade Docker Desk
 To install Docker Desktop successfully, you must:
 
 - Meet the [general system requirements](_index.md#general-system-requirements).
-- Have a 64-bit version of Fedora 40 or Fedora 41.
+- Have a 64-bit version of Fedora 41 or Fedora 42.
 - For a GNOME desktop environment you must install AppIndicator and KStatusNotifierItem [GNOME extensions](https://extensions.gnome.org/extension/615/appindicator-support/).
 - If you're not using GNOME, you must install `gnome-terminal` to enable terminal access from Docker Desktop:
 

content/manuals/engine/install/fedora.md

@@ -28,7 +28,6 @@ Fedora versions:
 
 - Fedora 42
 - Fedora 41
-- Fedora 40
 
 ### Uninstall old versions
 

content/manuals/engine/install/ubuntu.md

@@ -54,7 +54,6 @@ versions:
 - Ubuntu Oracular 24.10
 - Ubuntu Noble 24.04 (LTS)
 - Ubuntu Jammy 22.04 (LTS)
-- Ubuntu Focal 20.04 (LTS)
 
 Docker Engine for Ubuntu is compatible with x86_64 (or amd64), armhf, arm64,
 s390x, and ppc64le (ppc64el) architectures.