MdePkg: Remove "assert" from SmmCpuRendevousLibNull.c

REF: https://bugzilla.tianocore.org/show_bug.cgi?id=3931

Some drivers will break down when they use
SmmWaitForAllProcessor() which from SmmCpuRendezvousLibNull.c.
Removing the code "ASSERT(False)" will make consumer
work normally if they keep default setting for sync mode.

Cc: Michael D Kinney <michael.d.kinney@intel.com>
Cc: Liming Gao <gaoliming@byosoft.com.cn>

Signed-off-by: Zhihao Li <zhihao.li@intel.com>
Reviewed-by: Liming Gao <gaoliming@byosoft.com.cn>

MdePkg/Library/SmmCpuRendezvousLibNull/SmmCpuRendezvousLibNull.c

@@ -24,6 +24,5 @@ SmmWaitForAllProcessor (
   IN BOOLEAN  BlockingMode
   )
 {
-  ASSERT (FALSE);
   return EFI_SUCCESS;
 }