Unable to remove orphaned host

# Issue report

## What version of MicroCeph are you using ?
```
:~# snap list microceph
Name Version Rev Tracking Publisher Notes
microceph 18.2.4+snapc9f2b08f92 1139 reef/stable canonical✓ held
```
## What are the steps to reproduce this issue ?

1. Run `ceph osd tree`

## What happens (observed behaviour) ?
Once upon a time I had a host named `temp-member` in my cluster (as the name implies, temporarily). I can't recall exactly how I removed it from the cluster, but apparently the effort was incomplete, as the host still remains in the OSD tree list:
```
:~# ceph osd tree
ID CLASS WEIGHT TYPE NAME STATUS REWEIGHT PRI-AFF
-1 3.15599 root default
-4 1.29300 host home-server3
2 ssd 0.29300 osd.2 up 1.00000 1.00000
7 ssd 0.72769 osd.7 up 1.00000 1.00000
-3 1.86299 host home-server
8 1.86299 osd.8 up 1.00000 1.00000
-13 1.23179 host home-server2
6 ssd 1.23179 osd.6 up 1.00000 1.00000
-2 0 host temp-member
```

Microceph does not appear to be aware of this host anymore, which prevents me from interacting with it:
```
:~# microceph cluster list
+--------------+-------------------+-------+------------------------------------------------------------------+--------+
| NAME | ADDRESS | ROLE | FINGERPRINT | STATUS |
+--------------+-------------------+-------+------------------------------------------------------------------+--------+
| home-server3 | 192.168.1.124:7443| voter | .. | ONLINE |
+--------------+-------------------+-------+------------------------------------------------------------------+--------+
| home-server | 192.168.1.2:7443 | voter | .. | ONLINE |
+--------------+-------------------+-------+------------------------------------------------------------------+--------+
| home-server2 | 192.168.1.7:7443 | voter | .. | ONLINE |
+--------------+-------------------+-------+------------------------------------------------------------------+--------+
```

This host, of course, no longer exists, so All of the research I've found on this matter suggests that I need to use the ceph orchestrator to remove this host; however, this is of course not available in microceph (#434 , where it's expected that the `microceph` command is itself the orchestrator). This sort of leaves me between a rock and a hard place, since the solution is ostensibly to use `microceph`, but I can't since it doesn't see it.

## What were you expecting to happen ?
Only those hosts that are active appear.

## Relevant logs, error output, etc.
None that I can find.

## Additional comments.
I'm having another issue where I'm unable to join new hosts to my cluster. I'm not sure if this issue is related to that, but I'd like to clean this up regardless.

Thanks for your time and assistance here!

No source files or tests are named. Start by reproducing the reported `ceph osd tree` and `microceph cluster list` outputs, then review issue #434 and the host-removal behavior. Done means an orphaned `temp-member` entry can be removed or the supported recovery procedure is clearly documented.

Written by the indexing model from the issue text.