Fix the build
... by dropping the downstream libtool sed hack for removing rpaths.
This was causing the introspection scanner to pick up system libs
('libgnome-keyring.so.0: cannot open shared object file')
instead of the ones within the build tree.
Apparently the libtool in current libgnome-keyring tarball doesn't add any
lib64 rpaths, so we should be fine without the libtool hack.