Revert "libutils: Introduce StaticString16"

This reverts commit d4cb4894348818b90457d94580ed4d611c5d11b0.

Reason for revert: Breaking aosp_bonito-userdebug

Change-Id: Iea72f39d40f476002ce0ad6b5ce3b4e1ca570de7
diff --git a/libutils/SharedBuffer.h b/libutils/SharedBuffer.h
index 476c842..fdf13a9 100644
--- a/libutils/SharedBuffer.h
+++ b/libutils/SharedBuffer.h
@@ -102,12 +102,7 @@
         // Must be sized to preserve correct alignment.
         mutable std::atomic<int32_t>        mRefs;
                 size_t                      mSize;
-                uint32_t                    mReserved;
-public:
-        // mClientMetadata is reserved for client use.  It is initialized to 0
-        // and the clients can do whatever they want with it.  Note that this is
-        // placed last so that it is adjcent to the buffer allocated.
-                uint32_t                    mClientMetadata;
+                uint32_t                    mReserved[2];
 };
 
 static_assert(sizeof(SharedBuffer) % 8 == 0