Apply suggestions from code review

Co-authored-by: René <[email protected]>

Author: Renegade334

lib/internal/test_runner/mock/mock_timers.js

@@ -313,11 +313,7 @@ class MockTimers {
   }
 
   #restoreOriginalAbortSignalTimeout() {
-    if (this.#realAbortSignalTimeout) {
-      ObjectDefineProperty(AbortSignal, 'timeout', this.#realAbortSignalTimeout);
-    } else {
-      delete AbortSignal.timeout;
-    }
+    ObjectDefineProperty(AbortSignal, 'timeout', this.#realAbortSignalTimeout);
   }
 
   #createTimer(isInterval, callback, delay, ...args) {

test/parallel/test-mock-timers-abortsignal-timeout.js

@@ -4,20 +4,18 @@ require('../common');
 const assert = require('assert');
 const { mock } = require('node:test');
 
-{
-  mock.timers.enable({ apis: ['AbortSignal.timeout'] });
-
-  try {
-    const signal = AbortSignal.timeout(50);
-
-    assert.strictEqual(signal.aborted, false);
-
-    mock.timers.tick(49);
-    assert.strictEqual(signal.aborted, false);
-
-    mock.timers.tick(1);
-    assert.strictEqual(signal.aborted, true);
-  } finally {
-    mock.timers.reset();
-  }
-}
+const originalAbortSignalTimeout = AbortSignal.timeout;
+
+mock.timers.enable({ apis: ['AbortSignal.timeout'] });
+
+const signal = AbortSignal.timeout(50);
+assert.strictEqual(signal.aborted, false);
+
+mock.timers.tick(49);
+assert.strictEqual(signal.aborted, false);
+
+mock.timers.tick(1);
+assert.strictEqual(signal.aborted, true);
+
+mock.timers.reset();
+assert.strictEqual(AbortSignal.timeout, originalAbortSignalTimeout);