refactor: 닉네임 검증 중복 로직 제거

Author: larama-C

src/main/java/com/back/web7_9_codecrete_be/domain/auth/service/AuthService.java

@@ -170,9 +170,6 @@ public LoginResponse kakaoLogin(String code) {
     private User registerKakaoUser(KakaoUserInfo info) {
 
         String nickname = nicknameGenerator.generate();
-        if (userRepository.existsByNickname(nickname)) {
-            nickname = nickname + "_" + System.currentTimeMillis();
-        }
 
         User user = User.builder()
                 .email(info.getEmail())
@@ -222,9 +219,6 @@ public LoginResponse googleLogin(String code) {
     private User registerGoogleUser(GoogleUserInfo info) {
 
         String nickname = nicknameGenerator.generate();
-        if (userRepository.existsByNickname(nickname)) {
-            nickname = nickname + "_" + System.currentTimeMillis();
-        }
 
         User user = User.builder()
                 .email(info.getEmail())