Fixes after review

After discussion, we decided to simplify attribute translation for now. Full translation requires support for UTF-8 values encoded according to RFC 8187/7230, this can be clarified and implemented in further PRs.

1. Remove translation tables
2. Use simple translation rules only, for now ignoring UTF-8 keys and values

- `X-Attribute-NEOFS-` prefixed headers considered well-known system attributes
- System Attribute key is uppercased
- System Attribute key's `-` translates to `_`
- `X-Attribute-` prefixed headers considered regular object attributes
- Normal attribute key is a result of http header prefix trimming
- Value string should be left as is, for now

```
HTTP:
X-Attribute-NEOFS-Expiration-Epoch: 123
X-Attribute-FileName: cat.jpg

NeoFS:
__NEOFS__EXPIRATION_EPOCH: "123"
FileName: "cat.jpg"
```

Signed-off-by: Evgeniy Kulikov <kim@nspcc.ru>

settings.go

@@ -54,9 +54,6 @@ const (
 	cfgLoggerSamplingThereafter = "logger.sampling.thereafter"
 
 	// Uploader Header
-	cfgUploaderHeader                       = "uploader_header"
-	cfgUploaderHeaderKey                    = "key"
-	cfgUploaderHeaderVal                    = "val"
 	cfgUploaderHeaderEnableDefaultTimestamp = "upload_header.use_default_timestamp"
 
 	// Peers
@@ -187,13 +184,6 @@ func settings() *viper.Viper {
 		fmt.Printf("%s_%s_[N]_ADDRESS = string\n", Prefix, strings.ToUpper(cfgPeers))
 		fmt.Printf("%s_%s_[N]_WEIGHT = 0..1 (float)\n", Prefix, strings.ToUpper(cfgPeers))
 
-		fmt.Println()
-		fmt.Println("Upload Header Table:")
-		fmt.Println()
-
-		fmt.Printf("%s_%s_[N]_%s = string\n", Prefix, strings.ToUpper(cfgUploaderHeader), strings.ToUpper(cfgUploaderHeaderKey))
-		fmt.Printf("%s_%s_[N]_%s = string\n", Prefix, strings.ToUpper(cfgUploaderHeader), strings.ToUpper(cfgUploaderHeaderVal))
-
 		os.Exit(0)
 	case version != nil && *version:
 		fmt.Printf("NeoFS HTTP Gateway %s (%s)\n", Version, Build)