Clean up GraalVM metadata for HikariCP 6.0.0 tests

- Removed unnecessary "jni-config.json"; the test failure was unrelated to JNI and was caused by missing reflection metadata for "HikariConfig#getCredentials()".
- Trimmed "reflect-config.json" by removing "getExceptionOverride()" which is not accessed reflectively; confirmed the test still passes after removal.

Author: erguiti-imane

tests/src/com.zaxxer/HikariCP/6.0.0/src/test/resources/META-INF/native-image/tests-only/jni-config.json

@@ -1,11 +1,4 @@
 [
-  {
-    "name": "com.zaxxer.hikari.HikariConfig",
-    "methods": [
-      { "name": "getCredentials", "parameterTypes": [] },
-      { "name": "getExceptionOverride", "parameterTypes": [] }
-    ]
-  },
   {
     "name": "com.zaxxer.hikaricp.test.driver.CustomDriver",
     "methods": [