Remove version from cpio dependency

With backported version of cpio-gplv2 we have lesser version than the requested one. This is leading to unmets:

    2019/09/11 16:28:32 apt | The following packages have unmet dependencies:
    2019/09/11 16:28:32 apt |  initramfs-tools : Depends: initramfs-tools-core (= 0.132co1ba1) but it is not going to be installed
    2019/09/11 16:28:32 apt | E: Unable to correct problems, you have held broken packages.

The versioned depends was introduced for the --reproducible flag, used if SOURCE_DATE_EPOCH is set (which we don't use): https://salsa.debian.org/kernel-team/initramfs-tools/commit/f1cbe6f18c925cffd8529f04b3e71bbb26270dcc

Closes: https://phabricator.apertis.org/T6345