Remove the old ARM code generator from ART's Optimizing compiler.

The AArch32 VIXL-based code generator has been the default
ARM code generator in ART for some time now. The old ARM
code generator does not compile anymore; retiring it.

Test: test.py
Bug: 63316036
Change-Id: Iab8fbc4ac73eac2c1a809cd7b22fec6b619755db
diff --git a/compiler/optimizing/codegen_test.cc b/compiler/optimizing/codegen_test.cc
index fe25b76..0a8e97c 100644
--- a/compiler/optimizing/codegen_test.cc
+++ b/compiler/optimizing/codegen_test.cc
@@ -43,8 +43,7 @@
   ::std::vector<CodegenTargetConfig> v;
   ::std::vector<CodegenTargetConfig> test_config_candidates = {
 #ifdef ART_ENABLE_CODEGEN_arm
-    CodegenTargetConfig(kArm, create_codegen_arm),
-    CodegenTargetConfig(kThumb2, create_codegen_arm),
+    // TODO: Should't this be `kThumb2` instead of `kArm` here?
     CodegenTargetConfig(kArm, create_codegen_arm_vixl32),
 #endif
 #ifdef ART_ENABLE_CODEGEN_arm64