remove workflow created manually

.github/workflows/mkdoc.yml

@@ -1,22 +0,0 @@
-name: mkdocs
-on:
-  push:
-    paths:
-    - 'docs/**'
-
-jobs:
-  linux:
-    runs-on: ubuntu-latest
-    steps:
-    - uses: actions/checkout@v2
-    - name: Set up Python 3.8
-      uses: actions/setup-python@v1
-      with:
-        python-version: 3.8
-    - name: Install dependencies
-      run: |
-        python -m pip install --upgrade pip
-        pip install mkdocs
-    - name: Build doc
-      run: |
-        mkdocs gh-deploy