GITBOOK-150: Fix whitepaper link

Author: kenrogers

stacks-101/whitepapers.md

@@ -2,7 +2,5 @@
 
 In addition to the documentation here, there are numerous whitepapers detailing how the different pieces of the Stacks ecosystem work.
 
-* [Stacks 2.0](https://gaia.blockstack.org/hub/1AxyPunHHAHiEffXWESKfbvmBpGQv138Fp/stacks.pdf)
 * [Stacks Nakamoto Release](https://assets.stacks.co/stacks.pdf)
-* [Proof of Transfer](https://assets.website-files.com/5fcf9ac604d37418aa70a5ab/60072dbb32d416d6b3806935\_5f1596b12bcc0800f3dcadcd\_pox.pdf)
 * [sBTC](https://assets.stacks.co/sbtc.pdf)