Update tests after frame pointer refactoring

- Remove duplicate xref in cmd_zignature (better precision)
- Remove ARM64 frame pointer test from feat_variables (moved to dedicated test)

Author: vicky-dx

test/db/cmd/feat_variables

@@ -412,20 +412,3 @@ EXPECT=<<EOF
 8
 EOF
 RUN
-
-NAME=ARM64 frame pointer setup should not substitute variables
-FILE=malloc://1024
-ARGS=-a arm -b 64
-CMDS=<<EOF
-e asm.arch=arm
-e asm.bits=64
-wx fd7bbfa9fd030091  @ 0
-af @ 0
-pd 2 @ 0
-EOF
-EXPECT=<<EOF
-/ 12: fcn.00000000 ();
-|           0x00000000      fd7bbfa9       stp x29, x30, [sp, -0x10]!
-|           0x00000004      fd030091       mov x29, sp
-EOF
-RUN