We will bring the GTK 3 version to a more equal standing compared
to the GTK 4 one in the next commit.

This reverts commit 9f90c73.

In preparation for renaming wrapGAppsHook to wrapGAppsHook3.

GTK 3 is slowly approaching deprecation so let’s not make it default.

This was achieved using the following command:

    sd 'wrapGAppsHook\b' wrapGAppsHook3 (rg -l 'wrapGAppsHook\b')

And then manually reverted the following changes:

- alias in top-level.nix
- function name in wrap-gapps-hook.sh
- comment in postFixup of at-spi2-core
- comment in gtk4
- comment in preFixup of 1password-gui/linux.nix
- comment in postFixup of qgis/unwrapped-ltr.nix and qgis/unwrapped.nix
- comment in postFixup of telegram-desktop
- comment in postFixup of fwupd
- buildCommand of mongodb-compass
- postFixup of xflux-gui
- comment in a patch in kdePackages.kde-gtk-config and plasma5Packages.kde-gtk-config
- description of programs.sway.wrapperFeatures.gtk NixOS option (manual rebuild)

Now that there are no references in Nixpkgs.