docs: kernel-parameters.txt: Remove nompx

x86/mpx was removed in commit 45fc24e8
("x86/mpx: remove MPX from arch/x86"), this removes the documentation of
parameter nompx.

Fixes: 45fc24e8 ("x86/mpx: remove MPX from arch/x86")
Signed-off-by: Jimmy Assarsson <jimmyassarsson@gmail.com>
Acked-by: Dave Hansen <dave.hansen@linux.intel.com>
Link: https://lore.kernel.org/r/20200402172614.3020-1-jimmyassarsson@gmail.comSigned-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/admin-guide/kernel-parameters.txt

@@ -982,10 +982,6 @@
 			Documentation/admin-guide/dynamic-debug-howto.rst
 			for details.
 
-	nompx		[X86] Disables Intel Memory Protection Extensions.
-			See Documentation/x86/intel_mpx.rst for more
-			information about the feature.
-
 	nopku		[X86] Disable Memory Protection Keys CPU feature found
 			in some Intel CPUs.