UBIFS: kill CONFIG_UBIFS_FS_DEBUG_CHKS

Simplify UBIFS configuration menu and kill the option to enable self-check
compile-time. We do not really need this because we can do this run-time
using the module parameters or the corresponding sysfs interfaces. And
there is a value in simplifying the kernel configuration menu which becomes
increasingly large.
Signed-off-by: Artem Bityutskiy <Artem.Bityutskiy@nokia.com>

fs/ubifs/Kconfig

@@ -58,12 +58,3 @@ config UBIFS_FS_DEBUG
 	  down UBIFS. You can then further enable / disable individual  debugging
 	  features using UBIFS module parameters and the corresponding sysfs
 	  interfaces.
-
-config UBIFS_FS_DEBUG_CHKS
-	bool "Enable extra checks"
-	depends on UBIFS_FS_DEBUG
-	help
-	  If extra checks are enabled UBIFS will check the consistency of its
-	  internal data structures during operation. However, UBIFS performance
-	  is dramatically slower when this option is selected especially if the
-	  file system is large.