EomImage: Fix too early size-prepared emission

If an image without metadata support is loaded it could happen that
the size-prepared signal was emitted without knowing the actual
image size. That resulted in a smaller than necessary window size.
Remove unneeded emission since the loader will make sure to emit the
signal once the size is known.

https://bugzilla.gnome.org/show_bug.cgi?id=748598

origin commit:
https://gitlab.gnome.org/GNOME/eog/commit/5ae0b28

Author: fxri

src/eom-image.c

@@ -1032,8 +1032,6 @@ eom_image_real_load (EomImage *img,
 					break;
 				}
 
-				eom_image_emit_size_prepared (img);
-
 				priv->metadata_status = EOM_IMAGE_METADATA_NOT_AVAILABLE;
 			}