remove references to translation component and tooling for GNOME desktop shortcuts

[cfm]

Describe the change

freedomofpress/securedrop#6712 will remove the current GNOME desktop shortcuts in favor of a GNOME Shell extension, which can share translation catalogs and tooling with the main SecureDrop Web applications. The internationalization and translation documentation will need to be updated to reflect this change, in particular:

• Remove, and remove references to, the securedrop/desktop Weblate component
• Remove references to the i18n_tool.py --translate-desktop command

How will this impact users?

Translators will have one less Weblate component to monitor and update.

Localization Managers will have fewer commands to run during the localization cycle.