[DOCS] Clean up snippets and line number validation in docs

[cdkini]

Changes proposed in this pull request:

• Updated script to more thoroughly check for snippet line number violations
• Cleanup in docs and source code to fix certain snippet violations

Definition of Done

• [x] My code follows the Great Expectations style guide
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [x] I have made corresponding changes to the documentation

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