Clean up error codes and add error description for IRadioResponse 1.4.

Clean up some unneeded/confusing error codes in the 1.4 Radio HAL.
Quoting description from aosp/616923:

-Remove SYSTEM_ERROR. This is an ultra-generic error
 that also provides no meaningful distinction from
 INTERNAL_ERROR but is even less specified in scope.

-Remove NO_MEMORY. This is very implementation
 specific, and should be essentially impossible to
 hit in the generic sense. Today we don't have a
 generic EBUSY error code, which this would map to.
 Since it should be essentially impossible to hit,
 the preference is to assert that it shouldn't be.
 If an implementation really has memory pressure
 then it can return INTERNAL_ERROR, of which this
 is a class. INTERNAL_ERROR will be treated as a
 temporary failure anyway, making NO_MEMORY a
 distinction without a difference.

-Remove CANCELLED. We have no way to cancel an API
 call. If a persistent/ongoing request is cancelled
 by the caller using a separate API request, then
 that's a success case rather than an error case.

Bug: 73174777
Change-Id: I5bf268f86ed52e7294f7127f24beba04c9159fea
Test: Compilation