core: removing deprecated GetDiskConfigurationListQuery

GetDiskConfigurationListQuery is not used anymore by client:
Therefore, removing the following:
* GetDiskConfigurationListQuery
* GetDiskConfigurationListQueryTest
* DiskConfigurationList ConfigValue.

Change-Id: I8d750e63454096e4da0f7c4efdf229f7f06ac169
Signed-off-by: Daniel Erez <derez@redhat.com>