dropbear may drop scp support in future version

[abnoeh]

looks like dropbear's dev could remove support of scp command from 
itself becauss openssh command change scp's behavior to use sftp by 
default and it due to many bugs found by AI. currently it's still 
maintained, but he opened PR that remove scp from codebase. ( 
https://github.com/mkj/dropbear/pull/442 )

If this happends openwrt may need to uplift openssh into main and bundle 
openssh-sftp-server by default, (or they could make some minimal sftp 
support. I hope) while it's not happening right now I think this needs 
mention here as openwrt doesn't currently inlcude any sftp support by 
default