Bug 17044: Fix wrong destination for 'api' directory

Bug 17044: Fix wrong destination for 'api' directory

The original Makefile.PL tweak missed to trim the directory name thus
repeating the 'api' directory like in 'api/api'.

To test:
- Make a standard install (for example in /usr/share/koha
=> FAIL: check /usr/share/koha/api/api exists
- Make a single install (for example in /home/tcohen/koha-single)
=> FAIL: check /home/tcohen/koha-single/api/api exists
- Apply the patch
- Make a standard install (for example in /usr/share/koha
=> SUCCESS: check /usr/share/koha/api exists and doesn't contain a nested 'api' dir
- Make a single install (for example in /home/tcohen/koha-single)
=> SUCCESS: check /home/tcohen/koha-single/api exists and doesn't contain a nested 'api' dir
- Sign off :-D

Note: this affects the packages too, as the standard install is used as a basis.
Signed-off-by: Benjamin Rokseth <benjamin.rokseth@kul.oslo.kommune.no>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Brendan Gallagher <brendan@bywatersolutions.com>