Do not set AdbKeyStore to null when ADB is disabled

This will allow a user to clear adb authorizations after
disabling adb.

Fixes: 129469524
Test: Manually verified NPE did not occur after disabling adb
      and clearing authorizations.

Change-Id: Ia8a13c7011748a5a825e6fd07cc493593d479ba6
diff --git a/services/core/java/com/android/server/adb/AdbDebuggingManager.java b/services/core/java/com/android/server/adb/AdbDebuggingManager.java
index 8ccb6e2..9325d25 100644
--- a/services/core/java/com/android/server/adb/AdbDebuggingManager.java
+++ b/services/core/java/com/android/server/adb/AdbDebuggingManager.java
@@ -307,7 +307,6 @@
                     }
 
                     cancelJobToUpdateAdbKeyStore();
-                    mAdbKeyStore = null;
                     mConnectedKey = null;
                     break;