Drop our custom package
We currently fork WebKit to fix that one issue which affects both GTK and WebKitGTK: scrolling by swiping stops very early, making browing long views (web pages, directory with lots of files…) uncomfortable.
Given WebKit is a security sensitive component so it should always be up-to-date., hence it's better if we just take it from Debian instead of having this small fork.
For reference, here is a tentative clean fix for GTK: https://gitlab.gnome.org/GNOME/gtk/merge_requests/1226. This could help touchpads to behave similarly to touchscreens, allowing to simply drop the driction upstream: https://gitlab.freedesktop.org/libinput/libinput/merge_requests/293.