Compatibility: 5.0+
Expects: AX    4B04H  (INT 2fH)
BX    Switcher ID to be freed (obtained from INT 2fH 4B03H)
ES:DI Service-function address of task switcher to free
                                                                  
Returns: AX    0000H and...
BX    0000H if service was successful (else, invalid ID)
                                                                  
Info: Multiple task switchers may be active (see INT 2fH 4B03H).  When
one of them terminates, it must call this fn to notify the parent
(first) switcher that it is quitting.

This in NOT called by normal application programs--only by task
switchers.

- -

INT 2fH 4B04H: Free Switcher ID