display: fix off-guide image issues

display: fix off-guide image issues

The off-guide image does not scale and does not rotate
since "ui: reuse resource when it is reusable" commit has been applied.
Now showOffGuideImg() updates the geometry each time it is called.
And delete unnecessary code and clean up the off-guide image code.
The ancestor class of the QLabel, QWidget class, already has similar variable
and manipulation functions for the offGuideShown variable.

Change-Id: I5ae29e12ac2220842f312e3ae2d7cc0b19995d4c
Signed-off-by: Jinhyung Jo <jinhyung.jo@samsung.com>