Update referral-program.md

Remove USDT

Author: semuelle

docs/referral-program.md

@@ -3,6 +3,6 @@ sidebar_position: 7
 title: 💰 Referral Program
 ---
 
-We give away 500 USD, payable in USDC or USDT on Polkadot AssetHub, to each referral of a successful grant application by _anyone having previously worked on a Web3 Foundation grant_ or _a [Polkadot Ambassador](https://wiki.polkadot.network/docs/ambassadors)_. Web3 Foundation and Parity employees do not qualify for the program, even if they previously worked on a grant.
+We give away 500 USD, payable in USDC on Polkadot AssetHub, to each referral of a successful grant application by _anyone having previously worked on a Web3 Foundation grant_ or _a [Polkadot Ambassador](https://wiki.polkadot.network/docs/ambassadors)_. Web3 Foundation and Parity employees do not qualify for the program, even if they previously worked on a grant.
 
 In order to be eligible for the referral bonus, the application itself must contain the name of the [Polkadot Ambassador](https://wiki.polkadot.network/docs/ambassadors) or the GitHub account of the grantee as well as the payment address and currency of choice for the referral bonus (see the [application template](https://github.com/w3f/Grants-Program/blob/master/applications/application-template.md)).