dialer: Descend from GtkBin directly

Makes HdyDialer descend from GtkBin directly rather than from
GtkEventBox. GtkEventBox will be dropped in GTK+ 4 and brings no
functionality to HdyDialer.
3 jobs for dialer-bin in 7 minutes and 23 seconds (queued for 2 seconds)
Status Name Job ID Coverage
  Build
passed build-debian-clang #3805
librem5

00:02:52

passed build-debian-gcc #3804
librem5

00:02:11

24.8%
passed build-debian-package #3806
librem5

00:02:19