Remove the unnecessary template parameter from the class specialization

This seems to cause errors when compiling with gcc-11. Although this is
most likely a compiler bug, specifiying the template parameter type in
this case isn't necessary.

Fixes: QTBUG-91909
Fixes: QTBUG-90568
Pick-to: 6.0 6.1 5.15
Change-Id: Ib231257ccb2e16cc533f23ca5840d31e26a66d53
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/concurrent/qtconcurrentthreadengine.h

@@ -256,8 +256,8 @@ template <>
 class ThreadEngineStarter<void> : public ThreadEngineStarterBase<void>
 {
 public:
-    ThreadEngineStarter<void>(ThreadEngine<void> *_threadEngine)
-    :ThreadEngineStarterBase<void>(_threadEngine) {}
+    ThreadEngineStarter(ThreadEngine<void> *_threadEngine)
+        : ThreadEngineStarterBase<void>(_threadEngine) {}
 
     void startBlocking()
     {