tst_qrandomgenerator: replace QLinkedList with a std::list

In preparation of deprecating QLinkedList.

This actually simplifies the code, since std::list has a ctor from size,
which QLinkedList lacks, and which the code worked around by using
initializer_list.

Change-Id: I07f9d590f863d9e4e00de73339cdfa27079f6e03
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

tests/auto/corelib/global/qrandomgenerator/tst_qrandomgenerator.cpp

@@ -511,7 +511,7 @@ void tst_QRandomGenerator::generateNonContiguous()
     QFETCH(uint, control);
     RandomGenerator rng(control);
 
-    QLinkedList<quint64> list = { 0, 0, 0, 0,  0, 0, 0, 0 };
+    std::list<quint64> list(8);
     auto longerArrayCheck = [&] {
         QRandomGenerator().generate(list.begin(), list.end());
         return find_if(list.begin(), list.end(), [&](quint64 cur) {