Fix bazel build with -DTF_LITE_STATIC_MEMORY.

Tested that the following command passes:
```
bazel test tensorflow/lite/micro/...  --test_tag_filters=-no_oss --build_tag_filters=-no_oss --copt=-DTF_LITE_STATIC_MEMORY
```

Addresses http://b/175642155
diff --git a/tensorflow/lite/micro/micro_mutable_op_resolver.h b/tensorflow/lite/micro/micro_mutable_op_resolver.h
index 7a1015c..790b93b 100644
--- a/tensorflow/lite/micro/micro_mutable_op_resolver.h
+++ b/tensorflow/lite/micro/micro_mutable_op_resolver.h
@@ -36,6 +36,8 @@
 template <unsigned int tOpCount>
 class MicroMutableOpResolver : public MicroOpResolver {
  public:
+  TF_LITE_REMOVE_VIRTUAL_DELETE
+
   explicit MicroMutableOpResolver(ErrorReporter* error_reporter = nullptr)
       : error_reporter_(error_reporter) {}
 
@@ -421,8 +423,6 @@
   unsigned int GetRegistrationLength() { return registrations_len_; }
 
  private:
-  TF_LITE_REMOVE_VIRTUAL_DELETE
-
   TfLiteStatus AddBuiltin(tflite::BuiltinOperator op,
                           const TfLiteRegistration& registration,
                           MicroOpResolver::BuiltinParseFunction parser) {