libbinder: Suppress log spam when unlinking death recipients

Unlinking death recipients (from linkToDeath) is a normal part of Binder
operation, and doing it when a BpBinder's refcount has reached 0 is not
much different.

This log message is constantly spamming when swiping as part of a back
navigation gesture:

04-05 22:29:41.402   655  3888 I BpBinder: onLastStrongRef automatically unlinking death recipients: <uncached descriptor>
04-05 22:29:41.413   655  3888 I BpBinder: onLastStrongRef automatically unlinking death recipients: <uncached descriptor>
04-05 22:29:41.424   655  3888 I BpBinder: onLastStrongRef automatically unlinking death recipients: <uncached descriptor>
04-05 22:29:41.435   655   681 I BpBinder: onLastStrongRef automatically unlinking death recipients: <uncached descriptor>
04-05 22:29:41.447   655  3888 I BpBinder: onLastStrongRef automatically unlinking death recipients: <uncached descriptor>

Logging is relatively expensive on Android and the log spam isn't
useful, so suppress this log message by setting it to the verbose log
level.

Change-Id: I774d0c59ca6f70a4e2ed33b9fac3fb5b86d8ff0a
Signed-off-by: Simão Gomes Viana <devel@superboring.dev>