new-chat-dialog: Use HdyStatusPage for empty view

which makes the code simpler.
7 jobs for wip/sadiq/improve-empty-states in 8 minutes and 16 seconds
Status Job ID Name Coverage
  Build
passed #367258
librem5
build-pureos-gcc-byzantium

00:01:44

 
  Test
passed #367260
librem5
check-po

00:00:20

passed #367259
librem5
test:debian-gcc

00:01:34

22.5%
 
  Package
passed #367261
librem5
package-pureos-byzantium

00:01:35

passed #367262
librem5:arm64
package-pureos-byzantium:arm64

00:04:57

 
  Test Package
passed #367263
librem5
autopkgtest-pureos-byzantium-package

00:01:13

passed #367264
librem5
lintian-pureos-byzantium-package

00:00:42