Remove redundant PORTAGE_XATTR_EXCLUDE defaults (527636)

In install.py and movefile.py there were some redundant default
PORTAGE_XATTR_EXCLUDE settings. The default settings in make.globals
should be sufficient. Therefore, remove the redundant settings so that
we don't have to maintain them.

Fixes: 2fcdb5f36fac ("Add btrfs.* to default PORTAGE_XATTR_EXCLUDE (527636)")
X-Gentoo-Bug: 527636
X-Gentoo-Bug-URL: https://bugs.gentoo.org/show_bug.cgi?id=527636
Acked-by: Brian Dolbec <dolsen@gentoo.org>
Acked-by: Anthony G. Basile <blueness@gentoo.org>