Follow error prone recommendation

```
In SignedLongLong.java
47: warning: This assignment to the local variable 'lsb' is never read.
        long lsb = 0, msb = 0;
             ^
100: warning: Classes that override equals should also override hashCode
    public boolean equals(Object obj) {
                   ^
43: warning: A block tag has an empty description.
     * @throws UnsupportedEncodingException
       ^
100: warning: Prefer instanceof to getClass when implementing equals.
    public boolean equals(Object obj) {
                   ^
```

Bug: 236759221
Test: m RUN_ERROR_PRONE=true Bluetooth
Change-Id: Ie931ff50b3f7c7b4a5b5274d0244d2d57cad4319