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/compiler/debug/elf_debug_loc_writer.h b/compiler/debug/elf_debug_loc_writer.h
index 8cb4e55..4009acb 100644
--- a/compiler/debug/elf_debug_loc_writer.h
+++ b/compiler/debug/elf_debug_loc_writer.h
@@ -147,7 +147,7 @@
     DexRegisterLocation reg_hi = DexRegisterLocation::None();
     DCHECK_LT(stack_map_index, dex_register_maps.size());
     DexRegisterMap dex_register_map = dex_register_maps[stack_map_index];
-    DCHECK(dex_register_map.IsValid());
+    DCHECK(!dex_register_map.empty());
     CodeItemDataAccessor accessor(*method_info->dex_file, method_info->code_item);
     reg_lo = dex_register_map.GetDexRegisterLocation(vreg);
     if (is64bitValue) {