replace mustixes with actual phpisms_fixme by following the stack traces

Summary:
manually using scuba.

Will in the future do this more and once this lands we should be able to have a much better resolution for this

Reviewed By: mpomarole

Differential Revision: D5779018

fbshipit-source-id: 51bd697b6de589f67059f64e0a86f631734d3bc7

src/keyset/transform.php

@@ -82,12 +82,6 @@ function flatten<Tv as arraykey>(
 ): keyset<Tv> {
  $result = keyset[];
  foreach ($traversables as $traversable) {
- if (!PHPism_FIXME::isForeachable($traversable)) {
- FBLogger('phpism_fixme.invalid_foreach_arg')
- ->blameToPreviousFrame()
- ->mustfix('Attempting to foreach over a non-foreachable type');
- continue;
- }
  foreach ($traversable as $value) {
  $result[] = $value;
  }