fixup: remove flags function in perf tests

Author: dssgabriel

perf_tests/mpi/CMakeLists.txt

@@ -23,9 +23,6 @@ target_sources(
     test_2dhalo.cpp
     test_osu_latency.cpp
 )
-if(KOKKOSCOMM_ENABLE_TESTS)
-  kokkoscomm_add_cxx_flags(TARGET perf-test-main)
-endif()
 target_link_libraries(
   perf-test-main
   KokkosComm::KokkosComm