remove the "multithreading" qmake CONFIG parameter since OMP does not work for the Jamulus server because of too much threading overhead

Jamulus.pro

@@ -6,17 +6,6 @@ contains(CONFIG, "noupcasename") {
     TARGET = jamulus
 }
 
-# support multi-threading with OMP if requested
-contains(CONFIG, "multithreading") {
-    unix {
-        message(The OpenMP multithreading is enabled.)
-        message(NOTE THAT THE OpenMP IMPLEMENTATION IS STILL EXPERIMENTAL AND MAY NOT BE STABLE.)
-        DEFINES += USE_OMP
-        QMAKE_CXXFLAGS += -fopenmp
-        QMAKE_LFLAGS += -fopenmp
-    }
-}
-
 CONFIG += qt \
     thread \
     release

src/server.cpp

@@ -992,15 +992,6 @@ static CTimingMeas JitterMeas ( 1000, "test2.dat" ); JitterMeas.Measure(); // TE
                                                                  vecChannelLevels );
         }
 
-#ifdef USE_OMP
-// TODO This does not work as expected, the CPU is at high levels even if not much work is to be done. So we
-// have an issue using OMP in the OnTimer() function. Even if #pragma omp parallel for is used on a trivial
-// for loop for testing, still the CPU usage goes to very high values -> What is the cause of this issue?
-// NOTE Most probably it is the overhead of threads creation/destruction which causes this effect.
-// See https://software.intel.com/content/www/us/en/develop/articles/performance-obstacles-for-threading-how-do-they-affect-openmp-code.html
-// "[...] overhead numbers are high enough that it doesn’t make sense to thread that code. In those cases, we’re better off leaving the code in its original serial form."
-# pragma omp parallel for
-#endif
         for ( int i = 0; i < iNumClients; i++ )
         {
             int                iClientFrameSizeSamples = 0; // initialize to avoid a compiler warning