Remove db_impl_debug from release build

Summary:
Remove db_impl_debug from NDEBUG, but allow it in ROCKSDB_LITE
These functions by definition should not be included in NDEBUG and they are only used for testing
This is based on offline discussion with @yhchiang and @igor

Test Plan:
make static_lib
make check

Reviewers: igor, sdong, yhchiang

Reviewed By: yhchiang

Subscribers: igor, yhchiang, dhruba

Differential Revision: https://reviews.facebook.net/D48573

db/db_impl.h

@@ -254,7 +254,7 @@ class DBImpl : public DB {
   Iterator* NewInternalIterator(Arena* arena,
                                 ColumnFamilyHandle* column_family = nullptr);
 
-#ifndef ROCKSDB_LITE
+#ifndef NDEBUG
   // Extra methods (for testing) that are not in the public DB interface
   // Implemented in db_impl_debug.cc
 
@@ -305,7 +305,7 @@ class DBImpl : public DB {
 
   uint64_t TEST_LogfileNumber();
 
-#endif  // ROCKSDB_LITE
+#endif  // NDEBUG
 
   // Returns the list of live files in 'live' and the list
   // of all files in the filesystem in 'candidate_files'.

db/db_impl_debug.cc

@@ -7,7 +7,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file. See the AUTHORS file for names of contributors.
 
-#ifndef ROCKSDB_LITE
+#ifndef NDEBUG
 
 #include "db/db_impl.h"
 #include "util/thread_status_updater.h"
@@ -136,4 +136,4 @@ uint64_t DBImpl::TEST_LogfileNumber() {
 }
 
 }  // namespace rocksdb
-#endif  // ROCKSDB_LITE
+#endif  // NDEBUG