Revert "trusty: Mark vexpress-a15 target as 32-bit"

Revert submission 2403525-trusty-scudo-sdk

Reason for revert: Breaks gsa builds on polygon

Reverted changes: /q/submissionid:2403525-trusty-scudo-sdk

Change-Id: I488aa90ebc15bef9ea7a0a6c32d6781c24234bc0
diff --git a/project/vexpress-a15-trusty.mk b/project/vexpress-a15-trusty.mk
index 475b30f..2686874 100644
--- a/project/vexpress-a15-trusty.mk
+++ b/project/vexpress-a15-trusty.mk
@@ -17,8 +17,6 @@
 
 TARGET := vexpress-a15
 
-KERNEL_32BIT := true
-
 #
 # GLOBAL definitions
 #