Remove rustup installation

This installs in the wrong directory. Based on the CI job timings, at
most this would _maybe save us 30-60 seconds. The bulk of the remaining
time (4-5 minutes) is simply spent spinning up the VM, something we
can't really fix.

resources/provision.sh

@@ -100,25 +100,10 @@ setup_work_directory() {
   chown "$permissions" "$work_directory"
 }
 
-install_rust() {
-  curl --proto '=https' \
-    --tlsv1.2 \
-    --retry 10 \
-    --retry-connrefused \
-    --location \
-    --silent \
-    --show-error \
-    --fail "https://sh.rustup.rs" | \
-    sh -s -- --profile minimal -y --default-toolchain none
-
-  ~/.cargo/bin/rustup toolchain install 1.70 --profile minimal --no-self-update
-}
-
 setup_secondary_user
 configure_boot_flags
 configure_sendmail
 configure_boot_scripts
 install_extra_packages
-install_rust
 configure_sudo
 setup_work_directory