Remove snippet content size validation

What does this MR do?

In c02587ed we added a size limit validation to the snippet content. Now that we're moving towards version control snippets that check will be done in the GitAccessSnippet class.

Closes #210299 (closed)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• [ ] Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content