How to disable pin security from Samsing Tab 2
In my case, I installed my own certificate which even on removing was some where present don't know where so ultimately I cleared up every thing and again tried to remove pin and it got removed. 

Proper way would be settings-->security-->clear credential Clear credentials is last option under security heading.

And now u can change your pin  setting-->security-->screen lock-->swipe/none whatever you feel comfortable with.

Enjoy :D