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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def clear_file_systems(self):
 """Remove references to build and source file systems, reverting to the defaults"""


        self._source_url = None
        self.dataset.config.library.source.url = None
        self._source_fs = None

        self._build_url = None
        self.dataset.config.library.build.url = None
        self._build_fs = None

        self.dataset.commit()