Revert "Always create output_dir in setup_apprtc.py."

This reverts commit 52a8da38f9ec6da7c487626c699d811e542e1cf5.

Reason for revert: It doesn't solve the problem.

Original change's description:
> Always create output_dir in setup_apprtc.py.
> 
> This should probably fix [1]. It only happens on Windows bots and from
> the error it looks like if output_dir is missing, the unzipping just
> fails.
> 
> [1] - https://ci.chromium.org/p/chromium/builders/webrtc.fyi/WebRTC%20Chromium%20FYI%20Win%20Builder/4027
> 
> Bug: None
> Change-Id: I2f0abe90898d6d15525b46fd74635e2a3150cb37
> Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/151307
> Reviewed-by: Patrik Höglund <phoglund@webrtc.org>
> Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
> Cr-Commit-Position: refs/heads/master@{#29064}

TBR=phoglund@webrtc.org,mbonadei@webrtc.org

Change-Id: If8d93033dcb871476f23c1597f24efcd2e20cfb2
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: None
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/151420
Reviewed-by: Mirko Bonadei <mbonadei@webrtc.org>
Commit-Queue: Mirko Bonadei <mbonadei@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#29067}

rtc_tools/testing/setup_apprtc.py

@@ -29,9 +29,6 @@ def main(argv):
 
   output_dir = os.path.abspath(argv[1])
 
-  if not os.path.exists(output_dir):
-    os.makedirs(output_dir)
-
   download_apprtc_path = os.path.join(SCRIPT_DIR, 'download_apprtc.py')
   utils.RunSubprocessWithRetry([sys.executable, download_apprtc_path,
                                 output_dir])