More fixes to cabal description.
TeXMath writer:  Avoid double styling commands.

Test case:

<math display="block" xmlns="http://www.w3.org/1998/Math/MathML">
  <mrow>
    <mstyle mathvariant="script">
      <mi>ℱ</mi>
    </mstyle>
  </mrow>
</math>

Previously we got \mathcal{\mathcal{F}}, now we get \mathcal{F}.