Update smart-contracts-security.md

Author: Mikhail Dashkevich

blockchain/security/smart-contracts-security.md

@@ -25,7 +25,6 @@
 * How to recognize a scam token?
 * What are the risks of hacking the DAO?
 * What is reentrancy attack?
-* How to avoid airdrop scam?
 * What causes problems with rounding numbers?
 * Why is it important to test smart contracts? what is the difference between unit and integration tests?
 * Why is auditing important? Can it be trusted completely?