Revert "Use native async/await support in pub."

tools/run_pub.py

Index: tools/run_pub.py
diff --git a/tools/run_pub.py b/tools/run_pub.py
index c43b0396d85069441d93c70dca15d9630764ec9c..e11701d0cc19d9791d2eafa1fbc5bab4dc0355cc 100755
--- a/tools/run_pub.py
+++ b/tools/run_pub.py
@@ -12,7 +12,8 @@ import sys
 
 SCRIPT_DIR = os.path.dirname(sys.argv[0])
 DART_ROOT = os.path.realpath(os.path.join(SCRIPT_DIR, '..'))
-PUB_PATH = os.path.join(DART_ROOT, 'sdk/lib/_internal/pub/bin/pub.dart')
+PUB_PATH = os.path.join(DART_ROOT,
+                        'sdk/lib/_internal/pub_generated/bin/pub.dart')
 CANARY_PATH = os.path.join(DART_ROOT, 'tools', 'canary.dart')
 
 usage = """run_pub.py --package-root=<package root>"""
@@ -101,4 +102,4 @@ def main():
 
 
 if __name__ == '__main__':
-  sys.exit(main())
+  sys.exit(main());