yams #77664 dropschema2sql: must use dbhelper.sqls_drop_multicol_unique_index [validation pending]

case at hand: when using sqlserver, drop table will fail if the table has a View attached (and we use views to work around sqlserver limitations regarding NULL values in UNIQUE indexes). We need to call dbhelper.sqls_drop_multicol_unique_index in dropeschema2sql to handle this correctly.

This is important, because it prevents cwctl db-init -d to work on SQLServer.

done in0.34.0
load left0.000
closed by#6b9b6c81b9c5 pass a dbhelper to sqldropschema2sql to handle db specificities (closes #77664)