Fix invalid import add

[GuillaumeGomez]

Fixes gtk-rs/gtk#872
Fixes #735

cc @sdroege @EPashkin

[sdroege]

That's covering all of #735 ?

[GuillaumeGomez]

I didn't check on gstreamer. I doubt it'd work as is though. I can extend it if you want.

[sdroege]

Please do, would be nice to get rid of all those unused GString imports

[EPashkin]

@GuillaumeGomez You don't know which function added this import in calendar?
I don't see any function with string :(
I worry that we don't add import "String" in some cases (I not found that case in gtk-rs).

[GuillaumeGomez]

@EPashkin It's set_detail_func.

[GuillaumeGomez]

Ok, extended it a bit. Doesn't have warning on gstreamer-editing-services anymore.

@EPashkin I'm removing the imports from the callbacks only so that should be pretty accurate.

[EPashkin]

@GuillaumeGomez Now I understand that, thanks.

[EPashkin]

Last change broke gio's g_settings_schema_source_list_schemas

[GuillaumeGomez]

Interesting! I'll take a look.

[GuillaumeGomez]

It now works on gio as well. :)

[EPashkin]

@GuillaumeGomez Yes, not only needed changes. Thanks.

[EPashkin]

• now only needed changes

[EPashkin]

Lets merge