input: Write a python function to remove a key from the hash table if it exists.
  assert remove_key_from_hash_table({1: 1, 2: 2, 3: 3, 4: 4}, 3) == {1: 1, 2: 2, 4: 4}
  assert remove_key_from_hash_table({1: 1, 2: 2, 3: 3, 4: 4}, 5) == {1: 1, 2: 2, 3: 3, 4: 4}
  assert remove_key_from_hash_table({}, 1) == {}
output: def remove_key_from_hash_table(hash_table, key):
      if key in hash_table:
          del hash_table[key]
      return hash_table