Remove "SAFETY:" tag on comments that are not related to unsafe blocks

[DaniPopes]

Describe the feature

The // SAFETY: comment tag is used above unsafe blocks and impls to explain the need of its usage or why it's safe.

This is not always the case in this code base, where it's also used above calls to unwrap()/expect("...") explaining why it won't panic, and other places which are completely unrelated to unsafe.

These should be replaced with NOTE: or removed to make it just a normal comment.

Additional context

• Rust standard library guideline
• clippy::undocumented_unsafe_blocks
• clippy::missing_safety_doc
• zerocopy::safety_comment!

[TomAFrench]

This can be closed now.