manager: don't allow removing a device without traversing proper states

There was a special case for ensuring that the device's configuration
doesn't disappear when some factory is too late at recognizing the
device is just a component of another one.

It was always a bad idea. If the device already had an active
connection (such as for a generated default wired connection), it would
remain around, with a dangling reference to the device.

This effectively reverts commit 5ad69cb2 ('core: remove child devices
without deconfiguring them (bgo #738479)'). It's okay to do so, because
we now wouldn't deconfigure the device upon its removal anyway.
12 jobs for lr/no-allow_unmanage in 29 minutes and 53 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Test
passed #305819
allowed to fail
checkpatch

00:00:57

passed #305826
t_debian:9

00:14:29

passed #305828
t_debian:sid

00:22:47

manual #305827
allowed to fail manual
t_debian:testing
passed #305820
t_fedora:28

00:23:02

passed #305821
t_fedora:29

00:29:53

passed #305822
t_fedora:30

00:23:31

manual #305823
allowed to fail manual
t_fedora:rawhide
passed #305824
t_ubuntu:16.04

00:14:30

passed #305825
t_ubuntu:18.04

00:14:00

 
  External
passed NetworkManager test verification

passed NetworkManager test verification

05:53:56