Cleanup imports

p2p/discover: fix pending replies iteration

Range expressions capture the length of the slice once before the first
iteration. A range expression cannot be used here since the loop
modifies the slice variable (including length changes).

My temporary fix was merged upstream.

code.google.com/p/go.crypto is deprecated and will cause
problems in future versions of Go.

code.google.com/p/go.net is deprecated and will cause
problems in future versions of Go.

We forgot to update this reference when moving ecies into the
go-ethereum repo.