Follow error prone recommendation

```
In GsmAlphabet.java
28: warning: [InvalidInlineTag] Tag name `hide` is unknown.
 * {@hide}
   ^
312: warning: [InvalidBlockTag] Tag name `context` is unknown
     * @context the context to use to get the TelephonyManager
       ^
```

Bug: 236759221
Test: m RUN_ERROR_PRONE=true Bluetooth
Change-Id: If2d7b3cb555a82528a892f5354344d59937437dc