doc(readme): remove xtests section from readme

Signed-off-by: Sandro-Alessio Gierens <sandro@gierens.de>

README.md

@@ -271,44 +271,6 @@ The Nix Flake has a few features:
 - Run `nix build .#clippy` to lint with clippy (still work in progress).
 
 
-### Testing with Vagrant
-
-eza uses [Vagrant][] to configure virtual machines for testing.
-
-Programs such as eza that are basically interfaces to the system are [notoriously difficult to test][testing].
-Although the internal components have unit tests, it’s impossible to do a complete end-to-end test without mandating the current user’s name, the time zone, the locale, and directory structure to test.
-(And yes, these tests are worth doing. I have missed an edge case on many an occasion.)
-
-The initial attempt to solve the problem was just to create a directory of “awkward” test cases, run eza on it, and make sure it produced the correct output.
-But even this output would change if, say, the user’s locale formats dates in a different way.
-These can be mocked inside the code, but at the cost of making that code more complicated to read and understand.
-
-An alternative solution is to fake *everything*: create a virtual machine with a known state and run the tests on *that*.
-This is what Vagrant does.
-Although it takes a while to download and set up, it gives everyone the same development environment to test for any obvious regressions.
-
-[Vagrant]: https://www.vagrantup.com/
-[testing]: https://eev.ee/blog/2016/08/22/testing-for-people-who-hate-testing/#troublesome-cases
-
-First, initialise the VM:
-
-    host$ vagrant up
-
-The first command downloads the virtual machine image, and then runs our provisioning script, which installs Rust and eza’s build-time dependencies, configures the environment, and generates some awkward files and folders to use as test cases.
-Once this is done, you can SSH in, and build and test:
-
-    host$ vagrant ssh
-    vm$ cd /vagrant
-    vm$ cargo build
-    vm$ ./xtests/run
-    All the tests passed!
-
-Of course, the drawback of having a standard development environment is that you stop noticing bugs that occur outside of it.
-For this reason, Vagrant isn’t a *necessary* development step — it’s there if you’d like to use it, but eza still gets used and tested on other platforms.
-It can still be built and compiled on any target triple that it supports, VM or no VM, with `cargo build` and `cargo test`.
-
-</details>
-
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