Remove TextureManager / VectorAnimationManaver lifecycle observing

Remove TextureManager / VectorAnimationManaver lifecycle observing

Since we can use Dali::Adaptor::IsAvailable(), we don't need to check
whether manager itself is alive or not.

Since both of them are member value of VisualFactoryCache, and VisualFactory
is singletone class what will be destructed at Adaptor stop timing,
Dali::Adaptor::IsAvailabe() is enough.

Add/Remove observer will give some overhead for usual cases.
So just remove it, and check adaptor vailables intead.

Change-Id: Ib26df2d607d2871626cda956d86524f74afd424b
Signed-off-by: Eunki, Hong <eunkiki.hong@samsung.com>