input: Write a python function to manage inventory using the InventoryManager class.
  assert inv_manager.items == []
  inv_manager.add_item('apple')
  assert inv_manager.items == ['apple']
  inv_manager.add_item('banana')
  assert inv_manager.items == ['apple', 'banana']
  inv_manager.remove_item('apple')
  assert inv_manager.items == ['banana']
output: class InventoryManager:
      def __init__(self):
          self.items = []
  
      def add_item(self, item):
          self.items.append(item)
  
      def remove_item(self, item):
          if item in self.items:
              self.items.remove(item)