Remove legacy mode.

- Deleted the legacy WebSocket client implementation (`wstoclient.go`) and its test file (`wstoclient_test.go`).
- Removed legacy handling from the HTTP manager, including legacy proxy setup and routing.
- Cleaned up session management by removing legacy host checks and related functions.
- Eliminated the legacy WebRTC handler and its associated logic.
- Updated session interface to remove legacy methods.
- Removed legacy API documentation and configuration options from migration guide and help files.

server/internal/config/member.go

@@ -266,7 +266,7 @@ func (s *Member) Set() {
 }
 
 func (s *Member) SetV2() {
-	enableLegacy := false
+	deprecatedV2ConfigUsed := false
 
 	if viper.IsSet("password") || viper.IsSet("password_admin") {
 		s.Provider = "multiuser"
@@ -281,12 +281,10 @@ func (s *Member) SetV2() {
 			s.Multiuser.AdminPassword = "admin"
 		}
 		log.Warn().Msg("you are using v2 configuration 'NEKO_PASSWORD' and 'NEKO_PASSWORD_ADMIN' which are deprecated, please use 'NEKO_MEMBER_MULTIUSER_USER_PASSWORD' and 'NEKO_MEMBER_MULTIUSER_ADMIN_PASSWORD' with 'NEKO_MEMBER_PROVIDER=multiuser' instead")
-		enableLegacy = true
+		deprecatedV2ConfigUsed = true
 	}
 
-	// set legacy flag if any V2 configuration was used
-	if !viper.IsSet("legacy") && enableLegacy {
-		log.Warn().Msg("legacy configuration is enabled because at least one V2 configuration was used, please migrate to V3 configuration, visit https://neko.m1k1o.net/docs/v3/migration-from-v2 for more details")
-		viper.Set("legacy", true)
+	if deprecatedV2ConfigUsed {
+		log.Warn().Msg("deprecated V2 configuration is in use; migrate to V3 configuration, see https://neko.m1k1o.net/docs/v3/migration-from-v2")
 	}
 }