ssa_db_helper.c: Call removedir() only in case of old existing directory

Eliminates log messages:
removedir: ERROR - Couldn't open '.../smdb_dump' directory
when directory not present

Signed-off-by: Ilya Nelkenbaum <ilyan@mellanox.com>
Signed-off-by: Hal Rosenstock <hal@mellanox.com>