Removed synchronous image size getter

Removed synchronous image size getter

[problem]      Image::New() takes 1-4ms under load
[cause]        Each Image::New() calls GetClosestImageSize(), which performs
synchronous file i/o to load the image header.
[solution]     Removed this call and backed off to use the requested size or the
loaded size.  Application code that relies on image size being immediately set on
creation will break. (Image actors will no longer get their size set
automatically ).

Change-Id: Ide116312cf841a61e13993ff42b7c8399bb86ca7
Signed-off-by: David Steele <david.steele@partner.samsung.com>