[TD-3574]<fix>: Drop database operation is not completed when restarting, may cause taosd crash

src/dnode/src/dnodeMain.c

@@ -63,13 +63,16 @@ static SStep tsDnodeSteps[] = {
   {"dnode-vread",     dnodeInitVRead,      dnodeCleanupVRead},
   {"dnode-vwrite",    dnodeInitVWrite,     dnodeCleanupVWrite},
   {"dnode-vmgmt",     dnodeInitVMgmt,      dnodeCleanupVMgmt},
-  {"dnode-mread",     dnodeInitMRead,      dnodeCleanupMRead},
-  {"dnode-mwrite",    dnodeInitMWrite,     dnodeCleanupMWrite},
-  {"dnode-mpeer",     dnodeInitMPeer,      dnodeCleanupMPeer},  
+  {"dnode-mread",     dnodeInitMRead,      NULL},
+  {"dnode-mwrite",    dnodeInitMWrite,     NULL},
+  {"dnode-mpeer",     dnodeInitMPeer,      NULL},  
   {"dnode-client",    dnodeInitClient,     dnodeCleanupClient},
   {"dnode-server",    dnodeInitServer,     dnodeCleanupServer},
   {"dnode-vnodes",    dnodeInitVnodes,     dnodeCleanupVnodes},
   {"dnode-modules",   dnodeInitModules,    dnodeCleanupModules},
+  {"dnode-mread",     NULL,                dnodeCleanupMRead},
+  {"dnode-mwrite",    NULL,                dnodeCleanupMWrite},
+  {"dnode-mpeer",     NULL,                dnodeCleanupMPeer},  
   {"dnode-shell",     dnodeInitShell,      dnodeCleanupShell},
   {"dnode-statustmr", dnodeInitStatusTimer,dnodeCleanupStatusTimer},
   {"dnode-telemetry", dnodeInitTelemetry,  dnodeCleanupTelemetry},