Remove specific panic codes for ref-counting.

inc/ErrorNo.h

@@ -22,12 +22,6 @@ enum Error{
     MICROBIT_OOM = 20, 
 
     // Corruption detected in the micro:bit heap space
-    MICROBIT_HEAP_ERROR = 30,
-
-    // refcounter on an object is invalid (memory corruption)
-    MICROBIT_REF_COUNT_CORRUPTION = 31,
-
-    // refcounter was incremented/decremented after it already reached zero
-    MICROBIT_USE_AFTER_FREE = 32,
+    MICROBIT_HEAP_ERROR = 30
 };
 #endif

source/RefCounted.cpp

@@ -15,11 +15,9 @@ static inline bool isReadOnlyInline(RefCounted *t)
         return true; // object in flash
 
     // Do some sanity checking while we're here
-    if (refCount == 1)
-        uBit.panic(MICROBIT_USE_AFTER_FREE); // object should have been deleted
-
-    if ((refCount & 1) == 0)
-        uBit.panic(MICROBIT_REF_COUNT_CORRUPTION); // refCount doesn't look right
+    if (refCount == 1 ||        // object should have been deleted
+        (refCount & 1) == 0)    // refCount doesn't look right
+        uBit.panic(MICROBIT_HEAP_ERROR);
 
     // Not read only
     return false;