Do I need to remove my simm card to sell my ipad ?

A removable SIM card relates to your Cellular Airtime Contract. Yes, you should remove it if selling your device.

This information may be of help also.

What to do before you sell, give away, or trade in

your iPhone, iPad, or iPod touch

https://support.apple.com/en-us/HT201351

Only if it still has your active cellular service on it.

If you deactivated the service, or moved the service to another device, then its not necessary to remove the sim card. But you are free to do so if you want.

The new owner should provide their own anyway.