ci: avoid trying to cache cargo registry

There have been some very weird issues, where
cargo keeps fetching older commits of glib-rs
and breaking the build like so [1]

Might be stale cache, or some http/git mirroring
shenanigans, so lets stop trying to use the
cache for now and check if the issue persists.

[1]: https://gitlab.freedesktop.org/slomo/gst-plugins-rs/-/jobs/4715922

.gitlab-ci.yml

@@ -20,9 +20,6 @@ stages:
   variables:
     FDO_DISTRIBUTION_VERSION: 10
     FDO_DISTRIBUTION_TAG: '$RUST_VERSION-${GST_RS_IMG_TAG}_2020-04-28.1'
-    # Only stuff inside the repo directory can be cached
-    # Override the CARGO_HOME variable to force its location
-    CARGO_HOME: "${CI_PROJECT_DIR}/.cargo_home"
     FDO_BASE_IMAGE: "registry.freedesktop.org/gstreamer/gstreamer-rs/debian/10:$RUST_VERSION-$GST_RS_IMG_TAG"
   before_script:
     - source ./ci/env.sh
@@ -100,10 +97,6 @@ update-nightly:
 .dist-debian-container:
   extends:
   - .fdo.distribution-image@debian
-  cache:
-    key: "gst"
-    paths:
-      - "${CARGO_HOME}"
   variables:
     SODIUM_USE_PKG_CONFIG: "true"
   after_script: