node,blocksync,config: remove support for running nodes with blocksync disabled (#7159)

We stopped testing these configurations a while ago, and it doesn't
really make sense to allow nodes to run in this configuration. This
drops support for non-blocksync nodes and cleans up the
configuration/tests accordingly.

Closes: #6908

cmd/tendermint/commands/run_node.go

@@ -3,8 +3,6 @@ package commands
 import (
 	"bytes"
 	"crypto/sha256"
-	"errors"
-	"flag"
 	"fmt"
 	"io"
 	"os"
@@ -35,22 +33,7 @@ func AddNodeFlags(cmd *cobra.Command) {
 		"socket address to listen on for connections from external priv-validator process")
 
 	// node flags
-	cmd.Flags().Bool("blocksync.enable", config.BlockSync.Enable, "enable fast blockchain syncing")
 
-	// TODO (https://github.com/tendermint/tendermint/issues/6908): remove this check after the v0.35 release cycle
-	// This check was added to give users an upgrade prompt to use the new flag for syncing.
-	//
-	// The pflag package does not have a native way to print a depcrecation warning
-	// and return an error. This logic was added to print a deprecation message to the user
-	// and then crash if the user attempts to use the old --fast-sync flag.
-	fs := flag.NewFlagSet("", flag.ExitOnError)
-	fs.Func("fast-sync", "deprecated",
-		func(string) error {
-			return errors.New("--fast-sync has been deprecated, please use --blocksync.enable")
-		})
-	cmd.Flags().AddGoFlagSet(fs)
-
-	cmd.Flags().MarkHidden("fast-sync") //nolint:errcheck
 	cmd.Flags().BytesHexVar(
 		&genesisHash,
 		"genesis-hash",