Disabled variant still included in Count

[schultetwin1]

The additional attributes docs define the disabled attribute as:

disabled: removes variant from generated code.

However, when deriving the EnumCount trait, the disabled variant is still counted in the final count.

Here is some example code:

use strum::EnumCount;

#[derive(strum::EnumCount)]
enum Fields {
    Field0,
    Field1,
    Field2,
    #[strum(disabled)]
    Unknown,
}

fn main() {
    println!("Count: {}", Fields::COUNT);
}

Expected output: Count: 3
Actual output: Count: 4

This issue seems similar to #244