remove code cov check (AtsushiSakai#400)

Author: AtsushiSakai

.github/workflows/Linux_CI.yml

@@ -45,8 +45,6 @@ jobs:
       run: bash rundiffstylecheck.sh
     - name: do all unit tests
       run: bash runtests.sh
-    - name: Codecov
-      uses: codecov/[email protected]