[ci] Remove duplicate tests action

.github/workflows/unit-workflow.yml

@@ -1,14 +0,0 @@
-name: Unit tests
-on: [pull_request_target]
-
-jobs:
-  units:
-    runs-on: ubuntu-latest
-    steps:
-      - run: sudo apt-get install build-essential imagemagick libfreetype6-dev libjpeg-dev libpng-dev pkg-config
-      - uses: actions/checkout@v2
-        with:
-          submodules: 'recursive'
-      - run: make -j2 PLATFORM=simulator test.bin
-      - run: output/release/simulator/linux/test.bin
-