ldb: remove unpack only attr list functionality

ldb: remove unpack only attr list functionality

Unpack functions currently take an attribute list to restrict the set of
attributes to be returned in the constructed message. This
functionality is never used and complicates implementation of
forthcoming new pack format. This patch removes that functionality.
Using the unpack function then filtering the result turns
out not to be any slower.

NOTE: Configure with --abi-check-disable to build this commit. This
patch is part of a set of LDB ABI changes, and the version update is
done on the last commit.

Signed-off-by: Aaron Haslett <aaronhaslett@catalyst.net.nz>
Reviewed-by: Andrew Bartlett <abartlet@samba.org>
Reviewed-by: Gary Lockyer <gary@catalyst.net.nz>