export: fixed 'only' option printing one too many if printing header

python/obitools3/writers/tab.pyx

@@ -20,8 +20,6 @@ cdef class TabWriter:
             self.only = -1
         else:
             self.only = int(only)
-            if header:
-                self.only += 1
 
         self.formatter = formatter
         self.output = output_object