Deprecate the Metric worldtube format in CCE

[knelli2]

Proposed changes

We will be making it so that the CCE executable can only read Bondi modal data. In order to get your data into that format, all transitional functionality is moving to the ReduceCceWorldtube executable.

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• The code is documented and the documentation renders correctly. Run
  make doc to generate the documentation locally into BUILD_DIR/docs/html.
  Then open index.html.
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Further comments

Not sure if this was the best place for it, but there's already a warning in this option tag so I figured it'd be the best place and wouldn't be printed many times.