[arm64] Remove dead variables

GCC complained about these.

R=mstarzinger@chromium.org

Change-Id: I36d69b4191b63ae4373a9b96893cf98650acd7e9
Reviewed-on: https://chromium-review.googlesource.com/1206291Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55634}

test/cctest/test-assembler-arm64.cc

@@ -15068,9 +15068,6 @@ TEST(default_nan_double) {
 
 
 TEST(call_no_relocation) {
-  Address call_start;
-  Address return_address;
-
   INIT_V8();
   SETUP();
 
@@ -15091,9 +15088,7 @@ TEST(call_no_relocation) {
   __ Push(lr, xzr);
   {
     Assembler::BlockConstPoolScope scope(&masm);
-    call_start = buf_addr + __ pc_offset();
     __ Call(buf_addr + function.pos(), RelocInfo::NONE);
-    return_address = buf_addr + __ pc_offset();
   }
   __ Pop(xzr, lr);
   END();