Remove CHECK that GetThis() must always work.

Ensures GetVReg of a reference on compiled code checks that the
value is indeed a reference from the stack maps.

bug: 116683601
bug: 117452149
Test: 686-get-this
Change-Id: I3a370c45786a4892c7888491bec6d5ae64672f6c
diff --git a/runtime/interpreter/shadow_frame.h b/runtime/interpreter/shadow_frame.h
index 91371d1..88eb413 100644
--- a/runtime/interpreter/shadow_frame.h
+++ b/runtime/interpreter/shadow_frame.h
@@ -179,12 +179,8 @@
   mirror::Object* GetVRegReference(size_t i) const REQUIRES_SHARED(Locks::mutator_lock_) {
     DCHECK_LT(i, NumberOfVRegs());
     mirror::Object* ref;
-    if (HasReferenceArray()) {
-      ref = References()[i].AsMirrorPtr();
-    } else {
-      const uint32_t* vreg_ptr = &vregs_[i];
-      ref = reinterpret_cast<const StackReference<mirror::Object>*>(vreg_ptr)->AsMirrorPtr();
-    }
+    DCHECK(HasReferenceArray());
+    ref = References()[i].AsMirrorPtr();
     ReadBarrier::MaybeAssertToSpaceInvariant(ref);
     if (kVerifyFlags & kVerifyReads) {
       VerifyObject(ref);