Revert "tui: additional fix for 'primary' option"

It makes no sense -- the primary option is specific to active-backup bonds; not
mandatory. It blocks validation and prvents using other options.

This reverts commit 37f12088e45a663271e2ee6759a2b924c9745cd1.

https://bugzilla.redhat.com/show_bug.cgi?id=1142864