mgmt: mcumgr: Remove log management support from Kconfig

The commit removes a leftover configuration of the log management that
has never worked and has been removed with the commit
0bb466c34e4fe863733a929baa8f51981263ce3d to apache/mynewt-mcumgr.

Signed-off-by: Dominik Ermel <dominik.ermel@nordicsemi.no>