Revert "Convert to new override syntax (#357)"

This commit is not compatible with zeus layer so revert it.

This reverts commit bf6705fb7f.

Signed-off-by: Clément Péron <peron.clem@gmail.com>

classes/rust-bin.bbclass

@@ -1,6 +1,6 @@
 inherit rust
 
-RDEPENDS:${PN}:append:class-target = " ${RUSTLIB_DEP}"
+RDEPENDS_${PN}_append_class-target = " ${RUSTLIB_DEP}"
 
 RUSTC_ARCHFLAGS += "-C opt-level=3 -g -L ${STAGING_DIR_HOST}/${rustlibdir} -C linker=${RUST_TARGET_CCLD}"
 EXTRA_OEMAKE += 'RUSTC_ARCHFLAGS="${RUSTC_ARCHFLAGS}"'