Fix recalculating forms twice

Summary:
As a side effect of f0a80a67 a recalculation was triggered
by the notifyFormChanges called in EditFormTextCommand::redo,
which is called for each edit. So calculation was done twice.

Test Plan: The calculate forms test still passes.

Reviewers: aacid

Subscribers: okular-devel

Tags: Okular

Differential Revision: https://phabricator.kde.org/D12825