Update target_enable_mtl4.cmake

AMDiS/cmake3/target_enable_mtl4.cmake

@@ -5,8 +5,6 @@ macro(target_enable_mtl4 _TARGET_ _SCOPE_)
       set(LINK_EXECUTABLE OFF)
     endif ()
 
-    add_library(mtl4 INTERFACE)
-
     if (LINK_EXECUTABLE)
       target_include_directories(${_TARGET_} ${_SCOPE_} ${AMDIS_INCLUDE_DIR}/mtl4)
     else ()
@@ -21,7 +19,6 @@ macro(target_enable_mtl4 _TARGET_ _SCOPE_)
       endforeach ()
     endif (ENABLE_CXX11)
 
-
     if (ENABLE_OPENMP)
         find_package(OpenMP REQUIRED)
         if (OPENMP_FOUND)