Remove bogus pre-step inserts

These don't do anything. I've compared against some other Rust packages
(some ProxmoxVE stuff) and the output of debcargo against this crate
(from crates.io, now that it's up). Neither contain these targets. I'm
fairly confident I don't need them at all.

debian/rules

@@ -13,12 +13,3 @@ export DEB_CARGO_CRATE=$(DEB_SOURCE)_$(DEB_VERSION_UPSTREAM)
 
 %:
 	dh $@ --buildsystem=cargo
-
-execute_after_dh_auto_clean:
-	$(CARGO) clean
-	rm -rf $(CARGO_HOME)
-	rm -rf $(CARGO_REGISTRY)
-
-execute_before_dh_auto_configure:
-	$(CARGO) prepare-debian $(CARGO_REGISTRY) --link-from-system
-	rm -f Cargo.lock