ringer: Use libfeedback

This triggers e.g. haptic feeback as well and can later on be used
for LED feedback.

We can drop the audio theme setting completely since feedbackd picks up
the global GNOME setting.

Since feedbackd currently does not cancel gsound's via a cancellable
this might make the phone ring a bit too long atm but that will be fixed
on the feedbackd side
(https://source.puri.sm/Librem5/feedbackd/-/issues/10)

src/meson.build

@@ -31,7 +31,7 @@ calls_includes = [ top_include, src_include ]
 calls_deps = [ dependency('gobject-2.0', version: '>= 2.58'),
                dependency('gtk+-3.0'),
                dependency('libhandy-0.0', version: '>= 0.0.12'),
-               dependency('gsound'),
+               dependency('libfeedback-0.0'),
                dependency('libpeas-1.0'),
                dependency('gom-1.0'),
                dependency('libebook-contacts-1.2'),