MCOL-5367 Fix a bug introduced in MCOL-5021 (AUX column implementation).

In the implementation of MCOL-5021, an assert was added in
`WE_DMLCommandProc::processBatchInsertHwm()` that assumed the
`WriteEngine::TableMetaData` cache is uniform across the cluster.
However, this assumption is incorrect.

This bug caused undefined behaviour in ColumnStore resulting in bugs
such as MCOL-5367. In MCOL-5367, in a multi-node ColumnStore cluster,
an INSERT ... SELECT in a transaction with system variable
`columnstore_use_import_for_batchinsert=OFF/ON` did not show inserted
records when a SELECT query was issued. Assuming a 3-node cluster setup,
DMLProc only sends a given batch of records to be inserted to one of the
3 nodes, and not all nodes. As a result, the `WriteEngine::TableMetaData`
cache is only populated for that one node and is not uniform across the
cluster, causing the assert to fail.

As a fix, we simply remove this assert as it is redundant and should not
have been added in the first place.

writeengine/server/we_dmlcommandproc.cpp

@@ -2457,7 +2457,6 @@ uint8_t WE_DMLCommandProc::processBatchInsertHwm(messageqcpp::ByteStream& bs, st
 
   if (hasAUXCol)
   {
-    idbassert(auxColDBRootExtentInfo.size() == 1);
     colDBRootExtentInfo.insert(colDBRootExtentInfo.end(), auxColDBRootExtentInfo.begin(),
                                auxColDBRootExtentInfo.end());
   }