Mk/Uses/cargo.mk: Unbreak install with rust-nightly

Remove yet another install metadata file.  This should all be
replaced with --no-track once it is part of lang/rust.

rust-lang/cargo#7560

===> Checking for items in STAGEDIR missing from pkg-plist
Error: Orphaned: .crates2.json

Mk/Uses/cargo.mk

@@ -283,7 +283,9 @@ do-install:
 		--root "${STAGEDIR}${PREFIX}" \
 		--verbose \
 		${CARGO_INSTALL_ARGS}
+# Replace with --no-track once it is part of lang/rust 
 	@${RM} -- "${STAGEDIR}${PREFIX}/.crates.toml"
+	@${RM} -- "${STAGEDIR}${PREFIX}/.crates2.json"
 .  endfor
 .endif