[CodeQuality] Deprecate UnusedForeachValueToArrayKeysRector

[TomasVotruba]

Deprecates UnusedForeachValueToArrayKeysRector.

The rule is opinionated: wrapping the iterated expression in array_keys() makes the foreach harder to read, and harder to extend once the value is needed again - then the whole line has to be reverted back.

 class SomeClass
 {
     public function run()
     {
         $items = [];
-        foreach ($values as $key => $value) {
+        foreach (array_keys($values) as $key) {
             $items[$key] = null;
         }
     }
 }

Also removed from the code quality level.