Fix move ResizeableObject move constructor

It wasn't handling non-owned allocators correctly, which messed up using
the move constructor on aos StaticBuilders.

Change-Id: Ie751fd0a0c76db723b375aaec310de66b08a55b1
Signed-off-by: James Kuszmaul <james.kuszmaul@bluerivertech.com>
diff --git a/aos/flatbuffers/base.h b/aos/flatbuffers/base.h
index f99dbb8..387dbc3 100644
--- a/aos/flatbuffers/base.h
+++ b/aos/flatbuffers/base.h
@@ -99,13 +99,7 @@
   // Users do not end up using the move constructor; however, it is needed to
   // handle the fact that a ResizeableObject may be a member of an std::vector
   // in the various generated types.
-  ResizeableObject(ResizeableObject &&other)
-      : buffer_(other.buffer_),
-        owned_allocator_(std::move(other.owned_allocator_)),
-        allocator_(owned_allocator_.get()) {
-    other.buffer_ = {};
-    other.allocator_ = nullptr;
-  }
+  ResizeableObject(ResizeableObject &&other);
   // Required alignment of this object.
   virtual size_t Alignment() const = 0;
   // Offset from the start of buffer() to the actual start of the object in