Remove vendor folder

[volodymyrZotov]

This MR removes the vendor directory as project already uses go modules, so it's not necessary to keep vendor.

It also will make MR review way easier, after changing dependencies it won't make enormous changes in the vendor folder.

The followup PRs will update Dockerfile to install dependencies while building an image.

[moward98]

With no real way to test these changes, I gently approve