Remove mention of fast sync mode in Getting Started guide (#24300)

Author: tqpcharlie

docs/_getting-started/index.md

@@ -60,9 +60,6 @@ These are:
 
 - **Full**: Downloads all blocks (including headers, transactions, and receipts) and
 generates the state of the blockchain incrementally by executing every block.
-- **Fast**: Downloads all blocks (including headers, transactions and
-receipts), verifies all headers, and downloads the state and verifies it against the
-headers.
 - **Snap** (Default): Same functionality as fast, but with a faster algorithm.   
 - **Light**: Downloads all block headers, block data, and verifies some randomly.