edje_external: fix external icon handling

edje_external: fix external icon handling

External icons were handled with a global variable, which reason
to exist seem quite weird. It seems to me it was used to retain
some states of the actual parameters to get them later without having
access to the real parameters.

I don't really get how this would have worked with more than one
icon. When I tried to animate an external icon, with two states,
there were leaks and memory corruption... Now both are gone.

@fix