weston-launch: Fix warning on error() not being avaiable due to removal of header

Commit a1450a8a removed errno header but forgot to remove all error()
calls.

Signed-off-by: Marius Vlad <marius.vlad@collabora.com>
2 jobs for fix-error-warn in 57 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Container Prep
passed #253949
container_prep

00:00:24

 
  Build
passed #253950
build-native-meson

00:00:33