Bug 18780: Translatability: Get rid of exposed tt directive in masthead-langmenu.inc

Bug 18780: Translatability: Get rid of exposed tt directive in masthead-langmenu.inc

The file opac-tmpl/bootstrap/en/includes/masthead-langmenu.inc exposes following tt directive to translators:

"[%% IF ( ( opaclanguagesdisplay ) && ( ! one_language_enabled ) && "
"( languages_loop ) && ( OpacLangSelectorMode == 'both' || "
"OpacLangSelectorMode == 'top') ) %%] "

This patch fixes it.

To test:
- Apply patch
- Verify that language selector in OPAC (top of the page) works as expected
- Bonus test: create a new language 'aa-AA', verify that line above does not
show up in aa-AA-opac-bootstrap.po

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>