xlat lib: Remove out-dated comment

As of commit e1ea9290, if the attributes of an inner memory region
are different than the outer region, new page tables are generated
regardless of how "restrictive" they are. This patch removes an
out-dated comment still referring to the old priority system based
on which attributes were more restrictive.

Change-Id: Ie7fc1629c90ea91fe50315145f6de2f3995e5e00

include/lib/xlat_tables.h

@@ -150,12 +150,6 @@ typedef enum  {
 	MT_MEMORY,
 	/* Values up to 7 are reserved to add new memory types in the future */
 
-	/*
-	 * The following values are organised so that a clear bit gives a more
-	 * restrictive mapping than a set bit, that way a bitwise-and of two
-	 * sets of attributes will never give an attribute which has greater
-	 * access rights than any of the original attributes.
-	 */
 	MT_RO		= 0 << MT_PERM_SHIFT,
 	MT_RW		= 1 << MT_PERM_SHIFT,