lib: Removed MPILIB, MPILIB_EXTRA, and SIGNATURE prompts

As modules are expected to select MPILIB, MPILIB_EXTRA, and SIGNATURE,
removed Kconfig prompts.
Requested-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Dmitry Kasatkin <dmitry.kasatkin@intel.com>
Signed-off-by: James Morris <jmorris@namei.org>

lib/Kconfig

@@ -286,14 +286,14 @@ config CORDIC
 	  calculations are in fixed point. Module will be called cordic.
 
 config MPILIB
-	tristate "Multiprecision maths library"
+	tristate
 	help
 	  Multiprecision maths library from GnuPG.
 	  It is used to implement RSA digital signature verification,
 	  which is used by IMA/EVM digital signature extension.
 
 config MPILIB_EXTRA
-	bool "Multiprecision maths library - additional sources"
+	bool
 	depends on MPILIB
 	help
 	  Additional sources of multiprecision maths library from GnuPG.
@@ -301,7 +301,7 @@ config MPILIB_EXTRA
 	  but can be compiled if needed.
 
 config SIGNATURE
-	tristate "In-kernel signature checker"
+	tristate
 	depends on KEYS && CRYPTO
 	select CRYPTO_SHA1
 	select MPILIB