QTest::qWaitFor: make a comment terser

...and adjust it to its presence in the new QDeadlineTimer overload,
which sports nanoseconds granularity.

Change-Id: Ifa9658ca32c5dc4bef5cf36dec2e452174eebe1c
Reviewed-by: Ahmad Samir <a.samirh78@gmail.com>
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>
(cherry picked from commit dd5925fedb19c8fdb2601ec9eab6fb916341ff47)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/corelib/kernel/qtestsupport_core.h

@@ -25,9 +25,8 @@ qWaitFor(Functor predicate, QDeadlineTimer deadline = QDeadlineTimer(std::chrono
     if (predicate())
         return true;
 
-    // qWait() is expected to spin the event loop, even when called with a small
-    // timeout like 1ms, so we we can't use a simple while-loop here based on
-    // the deadline timer not having timed out. Use do-while instead.
+    // qWait() is expected to spin the event loop at least once, even when
+    // called with a small timeout like 1ns.
 
     using namespace std::chrono;