[NFC] Remove dinosaur function

[demeritcowboy]

Overview

CRM_Case_BAO_Case::recordActivityViaEmail() seems to predate the email processor and even seems unused in the old svn tree.

Either I'm missing something or I can't find anywhere this function is used. As a sanity check I tested the email processor still works.

[civibot]

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[seamuslee001]

Test fail unrelated and doing a grep i cannot find it at all merging