[remove] Remove deprecated NewInInitializerRector

[TomasVotruba]

Removes NewInInitializerRector, deprecated since 2026-04 in #7913. Follows the same cleanup as #8094.

The rule collapsed an optional dependency into a promoted property with a new default:

 class SomeClass
 {
-    private Logger $logger;
-
     public function __construct(
-        ?Logger $logger = null,
+        private ?Logger $logger = new NullLogger,
     ) {
-        $this->logger = $logger ?? new NullLogger;
     }
 }

The two forms are not equivalent. A default value applies only when the argument is omitted, so an explicit null still lands as null:

new SomeClass(null);
// before: $this->logger is NullLogger  (?? catches it)
// after:  $this->logger is null        (default never fires)

The property could never hold null before and can now, and Rector cannot see whether any caller passes null explicitly. That is the "depends on context" from the original deprecation.

It took six rounds of edge-case patching before it was given up on: #1737, #1740, #5971, #6599, #7545, #7546.

The rule was in no set and its tests were already removed with the deprecation, so this only drops the class plus its two now-obsolete phpstan.neon ignore entries.