remove a couple of wrong tests

models/reporting/xero/schema.yaml

@@ -889,8 +889,6 @@ models:
         data_type: numeric
         description: |
           Total of bank transaction tax inclusive, presented in GBP.
-        tests:
-          - not_null
 
       - name: total_amount_wo_tax_local_curr
         data_type: numeric
@@ -942,7 +940,6 @@ models:
           2.25GBP).
         tests:
           - not_negative
-          - not_null
 
       - name: line_amount_tax_inclusiveness
         data_type: character varying