search-tab: Don't handle clicks on inactive icon

search-tab: Don't handle clicks on inactive icon

The icon set as secondary icon of the search entry depends on whether
a search is active or not - clicking the icon should reset the entry
only in the former case. This is implemented by connecting/disconnecting
the 'secondary-icon-clicked' signal when updating the icon, but an
additional signal connection was left-over when refactoring the search
entry, resulting in clicks on the inactive icon removing the hint text.
Fix by removing the stray signal connection.

https://bugzilla.gnome.org/show_bug.cgi?id=646855