Bug 1317478 - Use cargo from the rustc package.
The stable cargo now has all the features we need; pulling
a separate cargo nightly package is unnecessary.
MozReview-Commit-ID: FqWvSK0swsQ
--- a/build/mozconfig.rust
+++ b/build/mozconfig.rust
@@ -1,10 +1,10 @@
# Options to enable rust in automation builds.
# Tell configure to use the tooltool rustc.
# Assume this is compiled with --enable-rpath so we don't
# have to set LD_LIBRARY_PATH.
RUSTC="$topsrcdir/rustc/bin/rustc"
-CARGO="$topsrcdir/cargo/bin/cargo"
+CARGO="$topsrcdir/rustc/bin/cargo"
# Enable rust in the build.
ac_add_options --enable-rust
