lib/bb/{data, siggen}: Don't warn on SkipRecipe exceptions
Recipes/variables that raise a SkipRecipe exception are intentionally
skipped, and should not generate warnings.
[YOCTO #11319]
Signed-off-by: Nathan Rossi <nathan@nathanrossi.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>