Remove unused local variable

Resolves issue during `make pep8`:

F842 local variable 'cs' is annotated but never used

src/azul/plugins/metadata/hca/indexer/aggregate.py

@@ -50,7 +50,6 @@ class HCAAggregate(Aggregate):
 
     @cached_property
     def cell_count(self) -> int:
-        cs: JSON
         return sum(cs['total_estimated_cells']
                    for cs in self.contents['cell_suspensions']
                    if cs['total_estimated_cells'] is not None)