hfsplus: remove unused routine hfsplus_attr_build_key_uni

The directory/file catalog b-tree equivalent, hfsplus_build_key_uni(),
is used by hfsplus_find_cat() for internal referencing between catalog
records.  There is no corresponding usage for attributes - attribute
records do not refer to one another.

Signed-off-by: Hin-Tak Leung <htl10@users.sourceforge.net>
Cc: Sougata Santra <sougata@tuxera.com>
Cc: Anton Altaparmakov <anton@tuxera.com>
Cc: Vyacheslav Dubeyko <slava@dubeyko.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>