[BUGFIX] Correct order of key / field deletion

Prevent a SQL error when deleting a key and the field belonging
to the key in the install tool at the same time.

Therefore the order for deleting keys and fields is changed from
field first and key second to key first and field second.

Resolves: #50450
Releases: 6.2
Change-Id: I30aff6ea6c2bf01dec6197eec8fd3aa7306cfcbb