chore(blockchain): remove tip exercise

- remove tip exercise from blockchain branch

subjects/blockchain/tip/README.md

@@ -1,17 +0,0 @@
-# Tip
-
-### Instructions
-
-Create a web page, `tip.html` that contains a `Connect` button that triggers a MetaMask window that asks the user to connect an account. Once connected, it displays the address of the wallet.
-
-Additionally, the page contains:
-
-- an input field (id:`address`)
-- a button (id:`tip`)
-
-Pressing on the button send the amount of 0.001701 ETH to the address in the input field.
-
-### Notions
-
-- [ethers : connecting to MetaMask](https://docs.ethers.io/v5/getting-started/#getting-started--connecting)
-- [MetaMask : getting started ](https://docs.metamask.io/guide/getting-started.html)