Fix some trivial warnings in WifiP2pDevice.java

Add some missing @Override annotations, and mark some constants
as unused.

Bug: 28799169
Change-Id: I1ddef87ecb089b62e299544ae94a21d10ef42d98
Test: Compiles.
(cherry picked from commit b41e74f41ea78a30b03f3a37a0f4afb0aa1e05b5)
1 file changed