Remove references to Snap! from the curriculum.

[VulpineAmethyst]

This pull request aims to remove references to Snap!, for several reasons.

1. Many students come in to this curriculum not having experience with Snap!, because either the class is using this curriculum for the whole school year or because the students joined the class for the second semester.
2. Snap! is not accessible to blind students, particularly as embedded images. Alt text would not help, particularly if this curriculum is their first exposure to programming.
3. Teachers are capable of incorporating these references independently of the curriculum, on an as-needed basis.

[Dan-TEALS]

This pull request addresses an issue that has been raised repeatedly for Python Full and Python Both classes. It appears to have removed all of the unneeded Snap! references in the lesson plan. A new issue will be opened to ensure the slide decks don't contain any references to Snap! since this pull request doesn't contain any PPT changes.