[Fix] Update Slow II and Paralyze II potency

[Xaver-DaRed]

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• I understand that if I do not agree to the following points by completing the checkboxes my PR will be ignored.
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• I have tested my code and the things my code has changed since the last commit in the PR and will test after any later commits.

What does this pull request do?

Adds what would have been the old merit bonuses to the spell potency.
Slow II: https://wiki.ffo.jp/html/3454.html
Paralyze II: https://wiki.ffo.jp/html/3453.html

Steps to test these changes

None. Spells slightly stronger.

[TeoTwawki]

I hadn't realized this got missed back when they stopped being merit spells