fix: postfix completions include nots prefix-expr

[A4-Tacks]

• Remove redundant fallback state in include_references

Example

Like is_foo, .not, .if

fn main() {
    let is_foo = true;
    !is_foo.$0
}

Before this PR

fn main() {
    let is_foo = true;
    !if is_foo {
        $0
    }
}

After this PR

fn main() {
    let is_foo = true;
    if !is_foo {
        $0
    }
}