Bug 35323: Fix hint for OpacMoreSearches HTML customization

Bug 35323: Fix hint for OpacMoreSearches HTML customization

There was some confusion on where this content appears.
This patch fixes the description shown as hint in the HTML
customizations tool when when the OpacMoreSearches entry is
selected.

To test:
* Before appyling the patch
* Add a new HTML customization for OpacMoreSearches
* Verif hint showing below the pull down
* Set a title and a publication date in the past
* Enter a short text, like "Koha" as content
* Save
* Go to the OPAC, verify text shows in the navigation
* Apply patch
* Verify hint is now correct

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Katrin Fischer <katrin.fischer@bsz-bw.de>
(cherry picked from commit ec95c63d417f0268c1aec5f8dc8e9985e601656e)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>