Also clean up libchromiumcontent in cibuild.

script/cibuild

@@ -12,6 +12,8 @@ SOURCE_ROOT = os.path.abspath(os.path.dirname(os.path.dirname(__file__)))
 
 def main():
   rm_rf(os.path.join(SOURCE_ROOT, 'out'))
+  rm_rf(os.path.join(SOURCE_ROOT, 'vendor', 'brightray', 'vendor', 'download',
+                     'libchromiumcontent'))
 
   run_script('bootstrap.py')
   run_script('cpplint.py')