chore: remove unused EFFECT_IS_UPDATING constant

[Rich-Harris]

this doesn't do anything

[github-actions]

Playground

pnpm add https://pkg.pr.new/svelte@16317

[dummdidumm]

...yet. in the async branch it's needed because there it's only set when it's an effect, not when it's a derived. So we should just keep it

[Rich-Harris]

I think that would be better expressed inside push_reaction_value:

-if (active_reaction !== null && active_reaction.f & EFFECT_IS_UPDATING) {
+if (active_reaction !== null && (!async_mode_flag || (active_reaction.f & DERIVED) !== 0)) {
  if (source_ownership === null) {
    source_ownership = { reaction: active_reaction, sources: [value] };
  } else {
    source_ownership.sources.push(value);
  }
}

To me that's a lot clearer than an EFFECT_IS_UPDATING flag (which aside from any async mode nuance suggests 'the effect is updating' rather than 'the thing that is updating is an effect'), and it'll be more obvious what change needs to happen when we remove async_mode_flag. Most importantly, it saves us a bitwise flag (we're running out of them).

But I can make that change on the async branch instead, so I'll close this