Workflow: Remove k210 support.

.github/workflows/doc-and-test.yml

@@ -18,7 +18,7 @@ jobs:
           components: rust-src, llvm-tools-preview
           target: riscv64gc-unknown-none-elf
       - name: Build doc
-        run: cd os && cargo doc --no-deps --verbose  --features "board_qemu"
+        run: cd os && cargo doc --no-deps --verbose
       - name: Deploy to Github Pages
         uses: peaceiris/actions-gh-pages@v3
         with:
@@ -66,5 +66,3 @@ jobs:
         run: cd os && make run TEST=1
         timeout-minutes: 10
 
-      - name: Build for k210
-        run: cd os && make build BOARD=k210