ls: use fewer xattr-related syscalls

ls: use fewer xattr-related syscalls

* src/ls.c: Do not include <selinux/selinux.h> or "smack.h".
Include <linux/attr.h> if HAVE_LINUX_ATTR_H, for XATTR_NAME_CAPS.
(free_ent): Use aclinfo_scontext_free to free f->scontext.
(getfilecon_cache): Remove; no longer needed.
(file_has_aclinfo_cache): Rename from file_has_acl_cache,
and use file_has_aclinfo instead of file_has_acl.  All uses changed.
(gobble_file): Use file_has_aclinfo instead of file_has_acl, so
that we get more info about the file before deciding whether to
issue further syscalls for it.  Let file_has_aclinfo worry about
smack and SELinux.  Call has_capability only if the xattr list
mentions XATTR_NAME_CAPS.