Add a regression test for EC bitmap recovery losing a parity chunk

src/test/test_blockstore_v1.cpp

@@ -145,14 +145,6 @@ struct bs_test_t
     }
 };
 
-static bool memcheck(uint8_t *buf, uint8_t byte, size_t len)
-{
-    for (size_t i = 0; i < len; i++)
-        if (buf[i] != byte)
-            return false;
-    return true;
-}
-
 // Check that journaled data corruption is preserved after flushing
 // TODO more variations:
 // - block 4k, block 16k