efl_ui_panes: fix not to consider content min size for legacy panes

Summary:
Since legacy panes did not consider its content's min size, the
content's min size calculation logic is not done for legacy panes.

Reviewers: zmike

Reviewed By: zmike

Subscribers: cedric, reviewers, committers

Tags: efl

Differential Revision: https://phab.enlightenment.org/D10372