Suggested by Marko on github pr #576

buf_all_freed only needs to be called once, not 3 times.

buf_all_freed will always return TRUE if it returns.
It will crash if any page was not flushed so its effectively
an assert anyway.

The following calls are likely redundant and could be removed:

		fil_flush_file_spaces(FIL_TYPE_TABLESPACE);
		fil_flush_file_spaces(FIL_TYPE_LOG);