#818 Hypothesis hiding by eh/he

[Guillaume Verdier]

Since [feature-requests:#371] was implemented, equalities rewritten by eh/he are hidden in some cases, based on the assumption that they are not useful anymore.
However, these tactics only rewrite the selected hypotheses. Therefore, the rewritten identifier may still appear in the unselected hypotheses (while the equality has been hidden).
The tactics should be smarter and only hide the rewritten equality if the rewritten identifier does not appear in the unselected hypotheses. Otherwise, the equality should be unselected, not hidden.

[Guillaume Verdier]

Hiding/deselecting equalities has been improved as suggested. The changes have been merged in commit [a89c80].