Bug 18781: Translatability: Get rid of exposed tt directives in openlibrary-readapi.inc

The file koha-tmpl/opac-tmpl/bootstrap/en/includes/openlibrary-readapi.inc
exposes template directives to translation. The only string that should
appear in .po from this file is "Open Library: "

To test:
- Apply patch
- Verify that code changes make sense
- Bonus test: create a new language 'aa-AA', verify in aa-AA-opac-bootstrap.po
  that there is only the following string for openlibrary-readapi.inc:
msgid "Open Library: "
msgstr ""

NOTE: Followed a test plan similar to bug 18776 comment 3

Signed-off-by: Mark Tompsett <mtompset@hotmail.com>

Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
(cherry picked from commit 23cc8b3968)
Signed-off-by: Fridolin Somers <fridolin.somers@biblibre.com>

koha-tmpl/opac-tmpl/bootstrap/en/includes/openlibrary-readapi.inc

@@ -1,10 +1,4 @@
-[%# Input params:
-    bib - search result biblio record
-%]
-[% IF OpenLibrarySearch && (
-        bib.normalized_isbn ||
-        bib.lccn ||
-        bib.normalized_oclc
-) %]
+[%# Input params: bib - search result biblio record %]
+[% IF OpenLibrarySearch && ( bib.normalized_isbn || bib.lccn || bib.normalized_oclc ) %]
     <div class="ol_readapi_book" isbn="[% bib.normalized_isbn %]" lccn="[% bib.lccn %]" oclc="[% bib.normalized_oclc %]">Open Library: </div>
 [% END %]