[ticket/10917] Variable used only once so delete it

The variable $this->unequal_version was only used once and only to
display the version the package updates to. To display the version it
updates to makes no sense when the update files aren't meant to update
from the current version. (It's already shown in an error message) So I
deleted the variable from there.

Furthermore the use of version_compare makes the variable useless in
that context which is why I deleted the variable from the whole file and
replaced it in the relevant if statement with the old comparison.

PHPBB3-10917