Revert "Add 'features' command to print available feature gates" (#6771)

This reverts commit 5caf4e4.

## Which problem is this PR solving?
- Since upstream PR
open-telemetry/opentelemetry-collector#12014 was
merged, we don't need our own command anymore

## Description of the changes
- Revert previous PR

## How was this change tested?
```
$ go run ./cmd/jaeger featuregate
```

Signed-off-by: Yuri Shkuro <github@ysh.us>

cmd/jaeger/main.go

@@ -4,15 +4,12 @@
 package main
 
 import (
-	"fmt"
 	"log"
 
-	"github.com/spf13/cobra"
 	"github.com/spf13/viper"
 
 	"github.com/jaegertracing/jaeger/cmd/internal/docs"
 	"github.com/jaegertracing/jaeger/cmd/jaeger/internal"
-	"github.com/jaegertracing/jaeger/cmd/jaeger/internal/features"
 	"github.com/jaegertracing/jaeger/internal/storage/v1/elasticsearch/mappings"
 	"github.com/jaegertracing/jaeger/pkg/config"
 	"github.com/jaegertracing/jaeger/pkg/version"
@@ -23,7 +20,6 @@ func main() {
 	command := internal.Command()
 	command.AddCommand(version.Command())
 	command.AddCommand(docs.Command(v))
-	command.AddCommand(featuresCommand())
 	command.AddCommand(mappings.Command())
 	config.AddFlags(
 		v,
@@ -34,14 +30,3 @@ func main() {
 		log.Fatal(err)
 	}
 }
-
-func featuresCommand() *cobra.Command {
-	return &cobra.Command{
-		Use:   "features",
-		Short: "Displays the list of supported features",
-		Long:  "The 'features' command shows all supported features in the current build of Jaeger.",
-		Run: func(_ *cobra.Command, _ []string) {
-			fmt.Print(features.DisplayFeatures())
-		},
-	}
-}