Bug 7361 Fix default option in encoding dropdown

Bug 7361 Fix default option in encoding dropdown

http://bugs.koha-community.org/show_bug.cgi?id=7361
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
This patch changes the pull down for encodings in staged marc import.

Before patch:
- Character encoding preselected was 'Default'
- 'Default' broke diacritics in utf-8 encoded files and was reported
  to not work correctly
- Selecting 'UTF-8' from the drop down worked

After patch:
- Character encoding preselected is 'UTF-8 (Default)'
- There is no longer a 'Default' option and no separate 'UTF-8'

Signed-off-by: Paul Poulain <paul.poulain@biblibre.com>
(cherry picked from commit 86d6e6d3de0a8d935802abe843f7ec407af1c759)

Signed-off-by: Chris Nighswonger <chris.nighswonger@gmail.com>