QVarLengthArray: remove unneeded copy in replace()

QVarLengthArray is neither implicitly shared, nor does it feature a
magic resize() on out-of-bounds.

Therefore, data() doesn't detach(), so 't' remains stable.

The only reason for the copy, then, would be if T wasn't
self-assignment-safe, but we don't support such types.

Remove the copy.

Change-Id: I8dd12e1c9b8131ae17d641354fe362554062b78d
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/corelib/tools/qvarlengtharray.h

@@ -1,6 +1,6 @@
 /****************************************************************************
 **
-** Copyright (C) 2016 The Qt Company Ltd.
+** Copyright (C) 2021 The Qt Company Ltd.
 ** Contact: https://www.qt.io/licensing/
 **
 ** This file is part of the QtCore module of the Qt Toolkit.
@@ -619,8 +619,7 @@ template <class T, qsizetype Prealloc>
 inline void QVarLengthArray<T, Prealloc>::replace(qsizetype i, const T &t)
 {
     verify(i);
-    const T copy(t);
-    data()[i] = copy;
+    data()[i] = t;
 }
 
 template <class T, qsizetype Prealloc>