tools: moveconfig: report when CONFIGs are removed by savedefconfig

This is a rare case, but there is still possibility that some CONFIG
is moved to the .config, but it is removed by "make savedefconfig".
(For example, it happens when the specified CONFIG has no prompt in
the Kconfig entry, i.e. it is not user-configurable.)

It might be an unexpected case.  So, display the log in this case
(in yellow color to gain user's attention if --color option is given).

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Reviewed-by: Joe Hershberger <joe.hershberger@ni.com>