ObjectProperty currently looks like this:

pub struct ObjectProperty<'a> {
    pub span: Span,
    pub kind: PropertyKind,
    pub key: PropertyKey<'a>,
    pub value: Expression<'a>,
    pub init: Option<Expression<'a>>, // for `CoverInitializedName`
    pub method: bool,
    pub shorthand: bool,
    pub computed: bool,
}

As I understand it, the init field is only used within parser as a temporary value, but final AST will always have this field as None.

It'd be ideal to remove this field for 2 reasons:

1. It adds 16 bytes to ObjectProperty, and ObjectProperty is extremely common in ASTs, so it's not an insignificant cost.
2. It's something of a footgun. Code should never set init field to anything other than None, but it currently can.