phosh-phone: Demote chatty to Recommends

The Debian GNOME team announced that they want to remove gtk2 from forky.

chatty is in the list of key packages because phosh-phone depends on it. I think the key packages algorithm is a bit too strong there. phosh-core is a required part of task-phosh-desktop but the other metapackages of meta-phosh aren't.

Because chatty is a key package, its dependencies are too. chatty depends on libpurple which is built by source pidgin. Pidgin is GTK2 but there is a "pre-alpha" of 3.0 that uses GTK4. I think we need to get the new version of Pidgin into Unstable soon and having Pidgin be autoremovable can help. (It felt a bit easier to get gimp 3 into Debian after gimp 2 and all its reverse depends were removed from Testing.)

The key package algorithm only applies to Depends and Build-Depends, not Recommends, so lowering phosh-phone's dependency on chatty to Recommends will allow both chatty and pidgin to be autoremovable.