vagrant: Remove unneeded netctl

netctl isn't used since Vagrant v2.2.10[1][2] and the users has been
given a fair chance to update now (>9 months).

Fix #112

[1] https://github.com/hashicorp/vagrant/blob/ee2a5daceec7f18accc59a69b84ced299a219188/CHANGELOG.md#2210-august-24-2020
[2] https://github.com/hashicorp/vagrant/pull/11400
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