Remove unused GetDexRegisterMap arguments.

They are no longer needed in the new encoding.

I reuse the local variables in most places to DCHECK the size
of the decoded register map.  This has one catch though:
We sometimes omit all dex registers, so the DCHECK should be
done only after checking if the map is empty (if applicable).

Test: test-art-host-gtest-stack_map_test
Change-Id: I94b67029842374bc8eb7c9e5eac76fc93a651f24
diff --git a/runtime/jit/jit.cc b/runtime/jit/jit.cc
index b7b779c..5a5634e 100644
--- a/runtime/jit/jit.cc
+++ b/runtime/jit/jit.cc
@@ -493,8 +493,7 @@
 
     // We found a stack map, now fill the frame with dex register values from the interpreter's
     // shadow frame.
-    DexRegisterMap vreg_map =
-        code_info.GetDexRegisterMapOf(stack_map, number_of_vregs);
+    DexRegisterMap vreg_map = code_info.GetDexRegisterMapOf(stack_map);
 
     frame_size = osr_method->GetFrameSizeInBytes();
 
@@ -510,10 +509,11 @@
     memory[0] = method;
 
     shadow_frame = thread->PopShadowFrame();
-    if (!vreg_map.IsValid()) {
+    if (vreg_map.empty()) {
       // If we don't have a dex register map, then there are no live dex registers at
       // this dex pc.
     } else {
+      DCHECK_EQ(vreg_map.size(), number_of_vregs);
       for (uint16_t vreg = 0; vreg < number_of_vregs; ++vreg) {
         DexRegisterLocation::Kind location = vreg_map.GetLocationKind(vreg);
         if (location == DexRegisterLocation::Kind::kNone) {