revise warn msg for retention with EWAA

[Rick-Methot-NOAA]

Concisely describe what has been changed/addressed in the pull request.

no Issue created. Simple revision of language to clarify how retention functions work with EWAA, New NOTE msg states that when using EWAA, the same body wt is used for discarded and retained fish for both length-retention and age-retention. i.e.

    if (seltype(f, 2) >= 1)
    {
      if (WTage_rd > 0)
      {
        warnstream << "Length-based retention will use the same empirical wtatage for discard and retained fish for fleet: " << f;
        write_message (NOTE, 0);

• Resolves issue #

What tests have been done?

none needed

Where are the relevant files?

<-- - [x] No test files are required for this pull request. -->

What tests/review still need to be done?

none

Is there an input change for users to Stock Synthesis?

<-- - [x] No, there was no input change. -->

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