minor #35880 [5.0] Remove some unused variables (fancyweb)

This PR was merged into the 5.0 branch.

Discussion
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[5.0] Remove some unused variables

| Q             | A
| ------------- | ---
| Branch?       | 5.0
| Bug fix?      | no
| New feature?  | no
| Deprecations? | no
| Tickets       | -
| License       | MIT
| Doc PR        | -

Some cleanup.

Commits
-------

1f953e4 [5.0] Remove some unused variables

src/Symfony/Component/HttpClient/Internal/HttplugWaitLoop.php

@@ -72,7 +72,7 @@ public function wait(?ResponseInterface $pendingResponse, float $maxDuration = n
                         goto check_duration;
                     }
 
-                    if ([$request, $promise] = $this->promisePool[$response] ?? null) {
+                    if ([, $promise] = $this->promisePool[$response] ?? null) {
                         unset($this->promisePool[$response]);
                         $promise->resolve($this->createPsr7Response($response, true));
                     }

src/Symfony/Component/String/UnicodeString.php

@@ -243,7 +243,7 @@ public function replace(string $from, string $to): AbstractString
                 $tail = substr($tail, \strlen($slice) + \strlen($from));
             }
 
-            $str->string = $result .= $tail;
+            $str->string = $result.$tail;
             normalizer_is_normalized($str->string) ?: $str->string = normalizer_normalize($str->string);
 
             if (false === $str->string) {

src/Symfony/Component/VarDumper/Cloner/VarCloner.php

@@ -28,7 +28,6 @@ protected function doClone($var)
         $pos = 0;                       // Number of cloned items past the minimum depth
         $refsCounter = 0;               // Hard references counter
         $queue = [[$var]];    // This breadth-first queue is the return value
-        $indexedArrays = [];       // Map of queue indexes that hold numerically indexed arrays
         $hardRefs = [];            // Map of original zval ids to stub objects
         $objRefs = [];             // Map of original object handles to their stub object counterpart
         $objects = [];             // Keep a ref to objects to ensure their handle cannot be reused while cloning