fix: fix annotation cannot be removed issue in examples/highlights.html

[hsqStephenZhang]

Description

• the rendition.annotations.remove method is not properly called in examples/highlights.html; has been fixed
• the highlights record under the main section should be removed after the removal of corresponding annotation, not a big problem, but I think it's better; has been updated
• format in highlights.html; has been update by VS Code's html formatter