Optimize logic in SliceLongerSpanToMatchShorterLength

Author: xtqqczze

src/libraries/System.Private.CoreLib/src/System/MemoryExtensions.cs

@@ -4990,11 +4990,8 @@ private static void SliceLongerSpanToMatchShorterLength<T>(ref ReadOnlySpan<T> s
             {
                 other = other.Slice(0, span.Length);
             }
-            else if (span.Length > other.Length)
-            {
-                span = span.Slice(0, other.Length);
-            }
-            Debug.Assert(span.Length == other.Length);
+
+            span = span.Slice(0, other.Length);
         }
 
         /// <summary>