FindPython: remove unnecessary if check

`list(REMOVE_DUPLICATES)` is safe on empty lists since 3.14.

Modules/FindPython/Support.cmake

@@ -777,9 +777,7 @@ function (_PYTHON_SET_LIBRARY_DIRS _PYTHON_SLD_RESULT)
       list (APPEND _PYTHON_DIRS "${_PYTHON_DIR}")
     endif()
   endforeach()
-  if (_PYTHON_DIRS)
-    list (REMOVE_DUPLICATES _PYTHON_DIRS)
-  endif()
+  list (REMOVE_DUPLICATES _PYTHON_DIRS)
   set (${_PYTHON_SLD_RESULT} ${_PYTHON_DIRS} PARENT_SCOPE)
 endfunction()