src/mds/MDSRank.cc: remove delete calls from handle_asok_command()

src/mds/MDSRank.cc: remove delete calls from handle_asok_command()

The allocated 'Formatter' passed to the function should be
freed by the caller to avoid missusage.

If handle_asok_command() free's the pointer to 'Formatter' to pass
an indication of an error back to the caller, it should have at least
set the pointer to NULL to work anyway.

Fix for:

CID 1316253 (#1 of 1): Use after free (USE_AFTER_FREE)
 deref_arg: Calling flush dereferences freed pointer f. (The dereference
 happens because this is a virtual function call.)

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>