Remove some obsolete FIXMEs.

encoding2.c

@@ -283,7 +283,6 @@ static const char *alignof_type(const char *type, size_t *align)
 		case '[':
 		{
 			const char *t = type;
-			// FIXME: aligned size
 			parse_array(&t, (type_parser)alignof_type, &align);
 			return t;
 		}

sarray2.c

@@ -143,7 +143,7 @@ PRIVATE void SparseArrayInsert(SparseArray * sarray, uint32_t index, void *value
 			init_pointers(newsarray);
 			sarray->data[i] = newsarray;
 			child = newsarray;
-		}// FIXME: Concurrency (don't CoW twice)
+		}
 		else if (child->refCount > 1)
 		{
 			// Copy the copy-on-write part of the tree