[STYLE] check python with flake8 (#424)

I've been using this locally to find errors without running tests, and now that we're using autopep8, it passes with minimal suppressions. This is also what turned up the issues with the tutorials, which were fixed in #422.

python/test/regression/test_performance.py

@@ -3,7 +3,6 @@ import sys
 
 import pytest
 import torch
-from numpy import record
 
 import triton
 import triton.language as tl