Add pyflakes to CI (#902)

* Add pyflakes to CI

* Remove unused imports

.github/workflows/ci.yaml

@@ -131,6 +131,22 @@ jobs:
           find . -iname '*.py' \
           | grep -v 'build/'  \
           | xargs -n 1 -P 1 -I{} -t sh -c 'yapf {} | diff - {}'
+
+  pyflakes:
+    runs-on: ubuntu-18.04
+
+    steps:
+    - uses: actions/checkout@v2
+    - name: Set up Python
+      uses: actions/setup-python@v2
+      with:
+        python-version: 3.6
+    - name: Install pyflakes
+      run: pip install pyflakes==2.3.1
+
+    - name: Run pyflakes
+      run: pyflakes examples/ tools/ src/ test/ doc/
+
   linux:
 
     runs-on: ${{ matrix.os }}

test/py/onnx_backend_test.py

@@ -4,7 +4,6 @@ if sys.version_info < (3, 0):
 
 import argparse
 import os
-import platform
 import unittest
 import onnx
 import onnx.backend.test

test/py/test_op.py

-import migraphx, array, sys
+import migraphx
 
 
 def test_add_op():