fix: remove unparsed markdown from copyright footer

[wdconinc]

Fixes #61. This doesn't aim to resolve the underlying copyright question pointed out in #61 (@klieret, what's "not accurate" about it?), but it fixes the parsing issue.

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[klieret]

Ah, regarding the "not accurate", I don't see anything that is based off of the carpentries (neither content nor framework), but I guess it says "originally". Anyway, doesn't matter :)

[klieret]

I'll leave this for @jonas-eschle to merge :)

[wdconinc]

As far as I can tell, the content of the git lesson is based on git-novice originally, making this a derived work. Someone went through and turned it from md to rst for rtd before swcarpentry did the same on their end :-)

[klieret]

Ah, you're right, I had only checked the python lesson! Makes a lot of sense then :)

[wdconinc]

Same with shell. (And apparently it's still md and the analysis essentials framework runs pandoc on it.)