cmd: migrate to urfave/cli/v2 (#24751)

This change updates our urfave/cli dependency to the v2 branch of the library.
There are some Go API changes in cli v2:

- Flag values can now be accessed using the methods ctx.Bool,
  ctx.Int, ctx.String, ... regardless of whether the flag is 'local' or
  'global'.

- v2 has built-in support for flag categories. Our home-grown category
  system is removed and the categories of flags are assigned as part of
  the flag definition.

For users, there is only one observable difference with cli v2: flags must now
strictly appear before regular arguments. For example, the following command is
now invalid:

   geth account import mykey.json --password file.txt

Instead, the command must be invoked as follows:

   geth account import --password file.txt mykey.json

cmd/utils/flags_legacy.go

@@ -20,15 +20,15 @@ import (
 	"fmt"
 
 	"github.com/ethereum/go-ethereum/eth/ethconfig"
-	"gopkg.in/urfave/cli.v1"
+	"github.com/ethereum/go-ethereum/internal/flags"
+	"github.com/urfave/cli/v2"
 )
 
-var ShowDeprecated = cli.Command{
+var ShowDeprecated = &cli.Command{
 	Action:      showDeprecated,
 	Name:        "show-deprecated-flags",
 	Usage:       "Show flags that have been deprecated",
 	ArgsUsage:   " ",
-	Category:    "MISCELLANEOUS COMMANDS",
 	Description: "Show flags that have been deprecated and will soon be removed",
 }
 
@@ -39,20 +39,22 @@ var DeprecatedFlags = []cli.Flag{
 
 var (
 	// (Deprecated May 2020, shown in aliased flags section)
-	NoUSBFlag = cli.BoolFlag{
-		Name:  "nousb",
-		Usage: "Disables monitoring for and managing USB hardware wallets (deprecated)",
+	NoUSBFlag = &cli.BoolFlag{
+		Name:     "nousb",
+		Usage:    "Disables monitoring for and managing USB hardware wallets (deprecated)",
+		Category: flags.DeprecatedCategory,
 	}
 	// (Deprecated July 2021, shown in aliased flags section)
-	LegacyMinerGasTargetFlag = cli.Uint64Flag{
-		Name:  "miner.gastarget",
-		Usage: "Target gas floor for mined blocks (deprecated)",
-		Value: ethconfig.Defaults.Miner.GasFloor,
+	LegacyMinerGasTargetFlag = &cli.Uint64Flag{
+		Name:     "miner.gastarget",
+		Usage:    "Target gas floor for mined blocks (deprecated)",
+		Value:    ethconfig.Defaults.Miner.GasFloor,
+		Category: flags.DeprecatedCategory,
 	}
 )
 
 // showDeprecated displays deprecated flags that will be soon removed from the codebase.
-func showDeprecated(*cli.Context) {
+func showDeprecated(*cli.Context) error {
 	fmt.Println("--------------------------------------------------------------------")
 	fmt.Println("The following flags are deprecated and will be removed in the future!")
 	fmt.Println("--------------------------------------------------------------------")
@@ -61,4 +63,5 @@ func showDeprecated(*cli.Context) {
 		fmt.Println(flag.String())
 	}
 	fmt.Println()
+	return nil
 }