sound-theme-freedesktop: Don't set PACKAGE_ARCH

* either fix build to prevent trying to access compiler or don't set
  PACKAGE_ARCH, signature is different for different MACHINEs
  e.g.
  List of dependencies for variable TUNE_ARCH changed from 'set(['X86ARCH32', 'X86ARCH64'])' to 'set([])'
  Hash for dependent task gettext_0.18.3.1.bb.do_populate_sysroot changed from 915bae004926e982f835d12f511a5f2b to 24c8263bb82124c9000fff3eab16d293

Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com>