QByteArray::remove(n,n): minor code cleanup

The result of d.begin() is only used in one of the branches, so
defining it outside both branches is a bit unmotivated; instead, drag
toRemove_start out of the else branch and reuse it in the then branch,
too.

Amends 358b7a9e74.

Pick-to: 6.5
Change-Id: I162d72de7097a1257c8a0a01b69c36fc87466114
Reviewed-by: Ivan Solovev <ivan.solovev@qt.io>
(cherry picked from commit 2831ce613fdaebe94e35a8afe45a057004548991)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 56c05f47f6a05433606ed4dfe8f882416148e704)

src/corelib/text/qbytearray.cpp

@@ -2384,13 +2384,12 @@ QByteArray &QByteArray::remove(qsizetype pos, qsizetype len)
     if (pos + len > d->size)
         len = d->size - pos;
 
-    auto begin = d.begin();
+    const auto toRemove_start = d.begin() + pos;
     if (!d->isShared()) {
-        d->erase(begin + pos, len);
+        d->erase(toRemove_start, len);
         d.data()[d.size] = '\0';
     } else {
         QByteArray copy{size() - len, Qt::Uninitialized};
-        const auto toRemove_start = d.begin() + pos;
         copy.d->copyRanges({{d.begin(), toRemove_start},
                            {toRemove_start + len, d.end()}});
         swap(copy);