Remove doc build from regular regression

This check is redundant in our CI since the bookrunner job already
builds the documentation. It is also often breaking the regression
job, maybe due to some disk requirement.

scripts/kani-regression.sh

@@ -100,14 +100,6 @@ FEATURES_MANIFEST_PATH="$KANI_DIR/tests/cargo-kani/cargo-features-flag/Cargo.tom
 cargo kani --manifest-path "$FEATURES_MANIFEST_PATH" --harness trivial_success
 cargo clean --manifest-path "$FEATURES_MANIFEST_PATH"
 
-# Check that documentation compiles.
-echo "Current disk usage:"
-df -h
-echo "Starting doc tests:"
-cargo doc --workspace --no-deps --exclude std
-echo "Disk usage after documentation build:"
-df -h
-
 echo
 echo "All Kani regression tests completed successfully."
 echo