solve_univariate: Simplify complex solutions
Revert "solve_univariate: fix issue arising from #7843"

This reverts commit 036786aee9985d9c239548df1f860f25cfa63e24.

The reverted commit didn't really fixed the issues from #7843.
The union was taking place a lot of places and the solution of
the reverted commit every where will make the code too unclean.
Last commit simplified, the complex values because of which #7843,
though the issue is not fixed but the values for which the issue was
occuring won't probably occur.