Bug 27876: took away redundant heading in OPAC full serial issues

Bug 27876: took away redundant heading in OPAC full serial issues

Changed <h2> to <h1> and deleted current <h1> to eliminate redundancy.

To test:
1) Apply patch
2) Go to OPAC
3) Go to opac-serial-issues.pl
4) Check there is only one main heading and it is <h1>

Sponsored-by: Catalyst IT
Signed-off-by: Henry Bolshaw <bolshawh@parliament.uk>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>