fix: remove misleading requirement comment on fake_chunk size

fake_chunk->size is not used in computing its value after backward
consolidation. It is actually overwritten by b->size + b->prev_size.

The original comment stated that fake_chunk->size must be in the
smallbins range, which is incorrect.

Author: D4R30

glibc_2.23/house_of_einherjar.c

@@ -39,7 +39,7 @@ int main()
 	size_t fake_chunk[6];
 
 	fake_chunk[0] = 0x00; // The prev_size vs. size check is of no concern, until GLIBC 2.26 P->bk->size == P->prev_size check
-	fake_chunk[1] = 0x100; // size of the chunk just needs to be small enough to stay in the small bin
+	fake_chunk[1] = 0x00; // Arbitrary value; fake_chunk->size is ignored during backward consolidation.
 	fake_chunk[2] = (size_t) fake_chunk; // fwd
 	fake_chunk[3] = (size_t) fake_chunk; // bck
 	fake_chunk[4] = (size_t) fake_chunk; //fwd_nextsize

glibc_2.24/house_of_einherjar.c

@@ -39,7 +39,7 @@ int main()
 	size_t fake_chunk[6];
 
 	fake_chunk[0] = 0x00; // The prev_size vs. size check is of no concern, until GLIBC 2.26 P->bk->size == P->prev_size check
-	fake_chunk[1] = 0x100; // size of the chunk just needs to be small enough to stay in the small bin
+	fake_chunk[1] = 0x00; // Arbitrary value; fake_chunk->size is ignored during backward consolidation.
 	fake_chunk[2] = (size_t) fake_chunk; // fwd
 	fake_chunk[3] = (size_t) fake_chunk; // bck
 	fake_chunk[4] = (size_t) fake_chunk; //fwd_nextsize