Revert: [llvm-mca] Flush the output stream before we start the analysis of a new code region. NFC

Not sure why, but it breaks buildbot clang-cmake-armv8-full.
It causes a failure in TEST 'Xray-armhf-linux :: TestCases/Posix/profiling-single-threaded.cc'.

llvm-svn: 334617

llvm/tools/llvm-mca/llvm-mca.cpp

@@ -523,7 +523,6 @@ int main(int argc, char **argv) {
 
     B.run();
     Printer.printReport(TOF->os());
-    TOF->os().flush();
   }
 
   TOF->keep();