Fix python syntax in tools/presubmit.py

Python List Comprehension does not need join() (alias of os.path.join).

Change-Id: I9d5a8610d88c35fd4e3cb101bc10b25c3d1dd7cf
Reviewed-on: https://chromium-review.googlesource.com/538453Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Loo Rong Jie <loorongjie@gmail.com>
Cr-Commit-Position: refs/heads/master@{#46027}

tools/presubmit.py

@@ -249,7 +249,6 @@ class CppLintProcessor(SourceFileProcessor):
       return True
 
     filters = ",".join([n for n in LINT_RULES])
-    command = [sys.executable, 'cpplint.py', '--filter', filters]
     cpplint = self.GetCpplintScript(TOOLS_PATH)
     if cpplint is None:
       print('Could not find cpplint.py. Make sure '
@@ -258,7 +257,7 @@ class CppLintProcessor(SourceFileProcessor):
 
     command = [sys.executable, cpplint, '--filter', filters]
 
-    commands = join([command + [file] for file in files])
+    commands = [command + [file] for file in files]
     count = multiprocessing.cpu_count()
     pool = multiprocessing.Pool(count)
     try: