rust: remove python3-native DEPENDS

rust: remove python3-native DEPENDS

This dependency has always existed in the oe-core recipes but isn't
explicitly needed here: the host Python is sufficient.

Note that rust-common still inherits on python3native[1] so this doesn't
yet actually have a meaningful change to the dependency tree.

[1] oe-core 4abd6ee9d48 ("rust-common.bbclass: rewrite toolchain wrappers in (native) python")

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Mathieu Dubois-Briand <mathieu.dubois-briand@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>