Merge pull request #1286 from sjwarner-bp/complex-number-topics

complex-numbers: remove 'classes' as topic

config.json

@@ -1110,7 +1110,6 @@
       "difficulty": 8,
       "slug": "complex-numbers",
       "topics": [
-        "classes",
         "floating_point_numbers",
         "mathematics"
       ],