classes/externalsrc: scale back warning to a plain note
It turns out that there are folks out there who use externalsrc in
normal builds and don't really need to be warned; additionally within
the extensible SDK or when using devtool, it shouldn't be a warning
situation. Thus, scale it back to a note (we can't use bb.note() here
since that wouldn't actually be piped through to the bitbake UI). Also
touch up the message a little bit.
Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
