elm_transit: remove unnecessary image preload invocation
If user uses image object with following step, then unnecessary preloading
related line is invocated in elm_image_file_set.
elm_image_file_set(obj, file, NULL)
The following is the preloading related line triggered by elm_image_file_set.
Moreover there is a flickering issue caused by the unnecessary preloading.
A test code is attached.
Use following test code. The flickering issue occurs with ELM_SCALE=10 ELM_ACCEL=gl ./test_transit
Reviewers: Hermet, jsuya
Reviewed By: Hermet, jsuya
Differential Revision: https://phab.enlightenment.org/D11364