ref(core): Simplify span end time computation

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

Author: Lms24

packages/core/src/tracing/sentrySpan.ts

@@ -366,8 +366,8 @@ export class SentrySpan implements Span {
    * device slept), and it can never be negative.
    */
   private _getEndTimeFromDuration(): number {
-    const performanceNow = this._startPerformanceNow == null ? undefined : safePerformanceNow();
-    if (performanceNow == null || this._startPerformanceNow == null) {
+    const performanceNow = safePerformanceNow();
+    if (this._startPerformanceNow == null || performanceNow == null) {
       return timestampInSeconds();
     }
     return this._startTime + (performanceNow - this._startPerformanceNow) / 1000;