depot-tools-native: fix INSANE_SKIP
Created by: kwavnet
as depot-tools already is a native only package, there isn't any use in defining BBCLASSEXTEND.
Futhermore native recipes do not have any kind of packaging, rendering the assignments of FILES:{PN}-dev and INSANE_SKIP:
{PN}-dev not applicable.
Remove any packaging related setting and just use INSANE_SKIP:${PN}. Fixes: ninja-linux64 from depot-tools-native was already stripped, this will prevent future debugging!