Remove --enable-extended from cross dist builder

Shouldn't have an effect on produced artifacts and otherwise is causing
issues where `-Zsave-analysis` is passed during tests but fails
compilation.

Author: alexcrichton

Cargo.lock

@@ -597,7 +597,6 @@ version = "0.28.0"
 dependencies = [
  "curl",
  "failure",
- "http",
  "percent-encoding 2.0.0",
  "serde",
  "serde_derive",

src/ci/docker/dist-i586-gnu-i586-i686-musl/Dockerfile

@@ -32,7 +32,6 @@ RUN sh /scripts/sccache.sh
 ENV RUST_CONFIGURE_ARGS \
       --musl-root-i586=/musl-i586 \
       --musl-root-i686=/musl-i686 \
-      --enable-extended \
       --disable-docs
 
 # Newer binutils broke things on some vms/distros (i.e., linking against