lint: Refactor pyflakes to use more consistent style.

In particular, we no longer pass in the full `by_lang` object and
expect it to pull out the Python piece.

tools/lint

@@ -115,7 +115,7 @@ def run():
     @linter_config.lint
     def pyflakes():
         # type: () -> int
-        failed = check_pyflakes(args, by_lang)
+        failed = check_pyflakes(by_lang['py'], args)
         return 1 if failed else 0
 
     @linter_config.lint

tools/linter_lib/pyflakes.py

@@ -31,13 +31,13 @@ def suppress_line(line: str) -> bool:
             return True
     return False
 
-def check_pyflakes(options, by_lang):
+def check_pyflakes(files, options):
-    # type: (Any, Dict[str, List[str]]) -> bool
+    # type: (List[str], Dict[str, Any]) -> bool
-    if len(by_lang['py']) == 0:
+    if len(files) == 0:
         return False
     failed = False
     color = next(colors)
-    pyflakes = subprocess.Popen(['pyflakes'] + by_lang['py'],
+    pyflakes = subprocess.Popen(['pyflakes'] + files,
                                 stdout=subprocess.PIPE,
                                 stderr=subprocess.PIPE)
     assert pyflakes.stdout is not None  # Implied by use of subprocess.PIPE