Bluetooth: Remove redundant ifdefs from keys.h

There is no need to ifdef type definitions and whole file is already
under (CONFIG_BLUETOOTH_SMP) || defined(CONFIG_BLUETOOTH_BREDR).

This improves file readability.

Change-Id: I9bcceb01023f75e016ad71873f87b3393a09fe26
Signed-off-by: Szymon Janc <ext.szymon.janc@tieto.com>