CI: Update for new rustdoc

Use the new rustdoc target instead of trying to recreate the
environment.

Signed-off-by: David Brown <[email protected]>

Author: d3zd3z

.github/workflows/docs.yml

@@ -50,17 +50,7 @@ jobs:
         working-directory: zephyr-rust-lang/docgen
         run: |
           # Note that the above build doesn't set Zephyrbase, so we'll need to do that here.
-          source ../../zephyr/zephyr-env.sh
-          rm -rf .cargo
-          mkdir .cargo
-          cd .cargo
-          ln -s ../../build/rust/sample-cargo-config.toml config.toml
-          cat config.toml
-          cd ..
-          pwd
-          ls -l
-          cargo doc
-          cd ..
+          west build -t rustdoc -b nrf52840dk/nrf52840 docgen
           mkdir docout
           mv build/rust/target/thumbv7em-none-eabi/doc docout/nostd
           cp docs/top-index.html docout/index.html