Fix javadoc links in SubscriptionManager and TelephonyManager

This CL cleans up some @code with @link in javadoc of APIs introduced for Android 15.

Before the flag has been advanced, we can only use @code to refer to other APIs since javadoc of API is not able to flagged. 

Bug: 316183370
Change-Id: Ied637383a68707828415520b0d8d41572787c443
Test: m -j offline-sdk-docs
Flag: EXEMPT javadoc clean up