Revert "Prevent exceptions from accumulating in REPL"

This reverts commit 0cd951f.

It is not a correct solution because it prevents printing the same exception twice.

Author: cwalther

py/obj.c

@@ -125,7 +125,6 @@ void mp_obj_print_exception(const mp_print_t *print, mp_obj_t exc) {
                     mp_printf(print, decompressed_block, block);
                 }
             }
-            mp_obj_exception_clear_traceback(exc);
         }
     }
     mp_obj_print_helper(print, exc, PRINT_EXC);