Revert "Ignore removing switch for mellanox platform due to known lim…

…itation (#1216)" (#1232)

What I did?

This reverts commit 62aa244.

Why I did this?

This commit introduces a race condition with would cause syncd crash. The issue happens when:

Syncd.m_sn has been freed
SAI send a port state change notification which will access Syncd.m_sn ===> causes crash

configure.ac

@@ -17,10 +17,6 @@ AX_ADD_AM_MACRO_STATIC([])
 
 AM_CONDITIONAL(SONIC_ASIC_PLATFORM_BAREFOOT,   test x$CONFIGURED_PLATFORM = xbarefoot)
 AM_CONDITIONAL(SONIC_ASIC_PLATFORM_BROADCOM,   test x$CONFIGURED_PLATFORM = xbroadcom)
-AM_CONDITIONAL(SONIC_ASIC_PLATFORM_MELLANOX,   test x$CONFIGURED_PLATFORM = xmellanox)
-
-AM_COND_IF([SONIC_ASIC_PLATFORM_MELLANOX],
-        AC_DEFINE([MELLANOX], [1], [Define to 1 on Mellanox Platform]))
 
 AC_ARG_ENABLE(debug,
 [  --enable-debug          turn on debugging],

syncd/Syncd.cpp

@@ -1,4 +1,3 @@
-#include "config.h"
 #include "Syncd.h"
 #include "VidManager.h"
 #include "NotificationHandler.h"
@@ -4730,15 +4729,7 @@ void Syncd::run()
 
     m_mdioIpcServer->stopMdioThread();
 
-    sai_status_t status = SAI_STATUS_SUCCESS;
-#ifdef MELLANOX
-    if (shutdownType != SYNCD_RESTART_TYPE_COLD)
-    {
-        status = removeAllSwitches();
-    }
-#else
-    status = removeAllSwitches();
-#endif
+    sai_status_t status = removeAllSwitches();
 
     // Stop notification thread after removing switch
     m_processor->stopNotificationsProcessingThread();