Remove redundant and unused message

- Remove 'reg_voluntarily'
- Remove 'user_unknown' in favor of 'unknown_user' - but move text from old 'user_unknown' to 'unknown_user'

Found by @Twonox

src/main/resources/messages/messages_tr.yml

@@ -1,8 +1,7 @@
 kick_antibot: 'AntiBot koruma modu aktif! Birkac dakika sonra tekrar girmeyi deneyin.'
-unknown_user: '&cVeritabaninda kullanici bulunamadi!'
+unknown_user: '&cBu oyuncu kayitli degil!'
 unsafe_spawn: '&cOyundan ciktigin yer guvenli degil, baslangic noktasina isinlaniyorsun.'
 not_logged_in: '&cGiris yapmadin!'
-reg_voluntarily: 'Kendini sunucuya kaydetmek icin komut kullan, "/register <sifre> <TekrarSifre>"'
 usage_log: '&cKullanim: /login <sifre>'
 wrong_pwd: '&cYanlis sifre!'
 unregistered: '&cKayit basariyla kaldirildi!'
@@ -19,7 +18,6 @@ login_msg: '&cLutfen giris komutunu kullanin "/login <sifre>"'
 reg_msg: '&3Lutfen kayit komutunu kullanin "/register <sifre> <TekrarSifre>"'
 usage_unreg: '&cKullanim: /unregister <sifre>'
 pwd_changed: '&2Sifre basariyla degistirildi!'
-user_unknown: '&cBu oyuncu kayitli degil!'
 password_error: '&cSifre eslesmiyor, tekrar deneyin!'
 password_error_nick: '&cSifrenize adinizi koyamazsiniz, lutfen farkli bir sifre secin...'
 password_error_unsafe: '&cSectiginiz sifre guvenli degil, lutfen farkli bir sifre secin...'
@@ -73,4 +71,4 @@ invalid_name_case: 'Oyuna %valid isminde katilmalisin. %invalid ismini kullanara
 # TODO incomplete_email_settings: 'Error: not all required settings are set for sending emails. Please contact an admin.'
 # TODO email_send_failure: 'The email could not be sent. Please contact an administrator.'
 # TODO recovery_code_sent: 'A recovery code to reset your password has been sent to your email.'
-# TODO recovery_code_incorrect: 'The recovery code is not correct! Use /email recovery [email] to generate a new one'
+# TODO recovery_code_incorrect: 'The recovery code is not correct! Use /email recovery [email] to generate a new one'