sys-libs/libxcrypt: Fix installation with USE="split-usr system".

sys-libs/libxcrypt: Fix installation with USE="split-usr system".

Do not install 3 unnecessary copies of full library (regular file) for each non-native ABI:
  /usr/$(get_libdir)/libcrypt.so
  /usr/$(get_libdir)/libowcrypt.so
  /usr/$(get_libdir)/libxcrypt.so

Do not install unnecessary symlinks for each ABI:
  /usr/$(get_libdir)/libcrypt.so.2
  /usr/$(get_libdir)/libowcrypt.so.2
  /usr/$(get_libdir)/libxcrypt.so.2

Do not use gen_usr_ldscript().

No changes for other combinations of USE flags.

Signed-off-by: Arfrever Frehtes Taifersar Arahesis <Arfrever@Apache.Org>
Signed-off-by: Patrick McLean <chutzpah@gentoo.org>