add explicit ddl for drop statements instead of inheriting the defaul…

…t from dbt-core

plugins/postgres/dbt/include/postgres/macros/relations/materialized_view/drop.sql

@@ -0,0 +1,3 @@
+{% macro postgres__drop_materialized_view(relation) -%}
+    drop materialized view if exists {{ relation }} cascade
+{%- endmacro %}

plugins/postgres/dbt/include/postgres/macros/relations/table/drop.sql

@@ -0,0 +1,3 @@
+{% macro postgres__drop_table(relation) -%}
+    drop table if exists {{ relation }} cascade
+{%- endmacro %}

plugins/postgres/dbt/include/postgres/macros/relations/view/drop.sql

@@ -0,0 +1,3 @@
+{% macro postgres__drop_view(relation) -%}
+    drop view if exists {{ relation }} cascade
+{%- endmacro %}