CA-407343: do not remove the VHD parent property after leaf coalesce

Long standing bug, introduced in

```
changeset:   1508:3c5a651ef2e4
user:        Andrei Lifchits <andrei.lifchits@citrix.com>
date:        Wed Feb 10 09:41:59 2010 -0800
summary:     CA-36637: fix the free space requirements calculation for the inline- and leaf-coalesce; plus:
```

The act of coalescing a leaf VHD into a parent does not make any
structural changes to the parentage of the VHD into which the data has
been coalesced. This, unnecessarily, introduced a race where a VDI
would report not having a parent until the next SR scan fixed it up.

Signed-off-by: Mark Syms <mark.syms@cloud.com>

Author: MarkSymsCtx

libs/sm/cleanup.py

@@ -2316,7 +2316,6 @@ def _doCoalesceLeaf(self, vdi):
         # garbage
 
         # update the VDI record
-        vdi.parent.delConfig(VDI.DB_VHD_PARENT)
         if vdi.parent.raw:
             vdi.parent.setConfig(VDI.DB_VDI_TYPE, vhdutil.VDI_TYPE_RAW)
         vdi.parent.delConfig(VDI.DB_VHD_BLOCKS)