Now that target config json is provided by rust-target-config.bbclass,
the need for the cross and crosssdk recipes is removed. Drop them and
simplify dependencies accordingly.
(From OE-Core rev: 4b54f5f52b33db4d2fe95c5faef033b6c6b37b7d)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>