defconfig: sdxlemur: Remove slub debug config

Remove CONFIG_SLUB_DEBUG_ON from debug variant for performance
reasons. Also remove redundant HARDENED_USERCOPY from debug config
since this gets copied over from the standard config.

Change-Id: I7c6fc8620290cf126ced046f82811e9e39bc2a60
Signed-off-by: Dennis Cagle <dcagle@codeaurora.org>