IDA Help: del_items

Convert item (instruction/data) to unexplored bytes.
The whole item (including the head and tail bytes) will be destroyed.
It is allowed to pass any address in the item to this function
     ea     - any address within the item to delete
     flags  - combination of DELIT_... constants
     nbytes - number of bytes in the range to be undefined
returns: 1-ok, 0-failure

success del_items(ea_t ea, long flags=0, long nbytes=1);

#define DELIT_SIMPLE    0x0000  // simply undefine the specified item
#define DELIT_EXPAND    0x0001  // propogate undefined items, for example
                                // if removing an instruction removes all
                                // references to the next instruction, then
                                // plan to convert to unexplored the next
                                // instruction too.
#define DELIT_DELNAMES  0x0002  // delete any names at the specified
                                // address range (except for the starting
                                // address). this bit is valid if nbytes > 1
#define DELIT_NOTRUNC   0x0004  // don't truncate the current function