libgphoto2: fix build

autoconf.bbclass forces building po dirs by copying po/Makefile.in.in. We have
to care for libgphoto2_port/po/Makefile.in.in too and have to remove
AM_PO_SUBDIRS() from configure.ac since that causes

| autoreconf: running: aclocal --system-acdir=/home/Superandy/tmp/oe-core-eglibc/work/armv7a-vfp-neon-angstrom-linux-gnueabi/libgphoto2-2.4.11-r2/libgphoto2-2.4.11/aclocal-copy/ --automake-acdir=/home/Superandy/tmp/oe-core-eglibc/sysroots/x86_64-linux/usr/share/aclocal-1.12 -I /home/Superandy/tmp/oe-core-eglibc/work/armv7a-vfp-neon-angstrom-linux-gnueabi/libgphoto2-2.4.11-r2/libgphoto2-2.4.11/auto-m4/ -I /home/Superandy/tmp/oe-core-eglibc/work/armv7a-vfp-neon-angstrom-linux-gnueabi/libgphoto2-2.4.11-r2/libgphoto2-2.4.11/m4m/ -I /home/Superandy/tmp/oe-core-eglibc/work/armv7a-vfp-neon-angstrom-linux-gnueabi/libgphoto2-2.4.11-r2/libgphoto2-2.4.11/auto-m4/ -I /home/Superandy/tmp/oe-core-eglibc/work/armv7a-vfp-neon-angstrom-linux-gnueabi/libgphoto2-2.4.11-r2/libgphoto2-2.4.11/m4m/ --force -I auto-m4 -I m4m
| configure.ac:230: error: `po-directories' is already registered with AC_CONFIG_COMMANDS.

Signed-off-by: Andreas Müller <schnitzeltony@googlemail.com>
Signed-off-by: Koen Kooi <koen@dominion.thruhere.net>