No unused code diagnostics

```haxe
class Main {
static function main() {
var x = 1;
var dead = x + 1;
deadCall();
}

@:pure static function deadCall():Void {
"dead";
}
}
```
There is almost no unused code after `4.3.0` (regression since 4.3.1)
Especially with `analyzer-optimize` enabled.
```
-cp src
-D analyzer-optimize
-main Main
--interp
--dce full
```

Start by running the provided Main example with -D analyzer-optimize, --interp, and --dce full, comparing the behavior with the stated 4.3.0 baseline. Trace how unused-code diagnostics and dead-code elimination handle the shown unused variable and @:pure deadCall() case; done means the regression is reproduced and unused code is diagnosed again without breaking the supplied compilation options.

Written by the indexing model from the issue text.