remove unneeded variables

Author: sungchun12

sqlmesh/core/linter/rules/builtin.py

@@ -283,7 +283,6 @@ def check_model(self, model: Model) -> t.Optional[t.List[RuleViolation]]:
         this_model_cron_next = model.cron_next(placeholder_start_date)
 
         violations = []
-        has_valid_upstream = False
         for upstream_model_name in model.depends_on:
             upstream_model = self.context.get_model(upstream_model_name)
 
@@ -307,10 +306,7 @@ def check_model(self, model: Model) -> t.Optional[t.List[RuleViolation]]:
                     )
                 )
             elif upstream_model_cron_next <= this_model_cron_next:
-                has_valid_upstream = True
-                break
-        if has_valid_upstream:
-            return None
+                return None
         return violations