Remove DB dependencies (#704)

* Remove database adapter in favor of external dependencies

* Prevent flit from installing all optional dependencies when testing build

* Remove MongoDB service during CI build

.github/workflows/build.yml

@@ -10,12 +10,6 @@ jobs:
       matrix:
         python_version: [3.7, 3.8, 3.9]
 
-    services:
-      mongo:
-        image: mongo:4.2
-        ports:
-          - 27017:27017
-
     steps:
     - uses: actions/checkout@v1
     - name: Set up Python
@@ -35,7 +29,7 @@ jobs:
     - name: Build and install it on system host
       run: |
         flit build
-        flit install --python $(which python)
+        flit install --deps none --python $(which python)
         python test_build.py
 
   release: