refactor(b038): Cleanup unused code in B038Checker (#448)

The unused code would introduce a bug when used, thus I believe it's
better to remove it.

bugbear.py

@@ -1623,11 +1623,6 @@ def visit_Call(self, node: ast.Call):
 
         self.generic_visit(node)
 
-    def visit_Name(self, node: ast.Name):
-        if isinstance(node.ctx, ast.Del):
-            self.mutations.append(node)
-        self.generic_visit(node)
-
     def visit(self, node):
         """Like super-visit but supports iteration over lists."""
         if not isinstance(node, list):

tests/b038.py

@@ -16,6 +16,7 @@
     print(elem)
     if elem % 2 == 0:
         some_other_list.remove(elem)  # should not error
+        del some_other_list
 
 
 some_list = [1, 2, 3]

tests/test_bugbear.py

@@ -976,10 +976,10 @@ def test_b038(self):
         print(errors)
         expected = [
             B038(11, 8),
-            B038(25, 8),
             B038(26, 8),
-            B038(40, 8),
-            B038(46, 8),
+            B038(27, 8),
+            B038(41, 8),
+            B038(47, 8),
         ]
         self.assertEqual(errors, self.errors(*expected))