I can only speak for the primary i work in, but i would say removing them really isnt necessary. We don't push any religion or present any as fact. It is done as "jews believe / sikhs believe / christians believe".
So the lesson would say "christians believe that Jesus is the son of god" rather than "jesus is the son of god".
They are not all about actual 'god' either. So for example the lesson last week was on faith leaders, and what did they have in common, what makes a good leader, what kind of leader would you want to be.
Some lessons are on religious buildings, why they have certain features etc. The kids also visit a mosque and a church and do art work based on that.
At christmas we did the story behind the christingle then made them. It helps them actually understand these things rather than just seeing them at nativity.
Its really interesting actually because we have a mix of christians / hindus / muslims / non religious in our class and they have had some really nice respectful conversations, and learnt a lot through each other.
I dont see the problem in knowing stuff.
Also to add to a pp above, we did have one pissed off mum who removed her child from religious worship and classes. Then wondered why her son wasn't in the carol service or nativity 