Remove dependency on Modern::Perl

We depend on the Modern::Perl module, which will turn on modern Perl
features and typical things that most Perl programs use anyway, such as
strict and warnings. The problem is that the Modern::Perl module is not
a core module, and often not part of your Perl installation.

Since we don't strictly need the Modern::Perl module in order to use
modern Perl features we are just limiting the ability to run the program
by depending on it. Remove the dependency and import the needed
functionality directly.

Signed-off-by: Marcus Karlsson <mk@acc.umu.se>