Now the following versions are installed:
> S | Name | Type | Version | Arch | Repository
> ---+---------+---------+-------------------+--------+-----------------------
> i | libzypp | package | 17.11.4-lp151.1.1 | x86_64 | openSUSE-Leap-15.1-Oss
> i+ | zypper | package | 1.14.27-lp151.1.2 | x86_64 | openSUSE-Leap-15.1-Oss
I could now remove my symlink from /usr/lib64/libzypp.so.1702 to
/usr/lib64/libzypp.so.1709.2.4 and zypper still works.