Remove backwards_compatibility CI job

The backwards_compatibility CI job runs the tests with the latest
migrations against the test suite from the previous version. While
testing the backwards compatibility of the migrations is important,
the current approach has problems that make it unfeasible in practice.

1. The CI job figures out the previous version by reading the VERSION
   file from Gitaly's repo. This version file appears to be unupdated
   in Gitaly's master branch. As it is, it points to 14.3.0-rc2 when
   in fact it should point to some release candidate of 14.4. This means
   the tests are not against the latest release but the one before that.

2. Some assertions the tests make fail with newer migrations even if
   everything would be fine with a real setup. Some tests haven't setup
   their test state to fully match the production setup, and thus fail
   when the newer migrations are applied. In the same fashion, some tests
   fail with newer migrations even if they've setup their test state
   correctly. They may however make assertions on how the state looks like
   after running some code, yet the new migrations cause the state to look
   different from the asserted state. As an example, Praefect's deletion
   handling was changed in gitlab-org/gitaly!3906. The new code removes all
   records of a repository when the repository is deleted. The old code
   testing deletion fails as it still expects the records to be in place.
   The new code is backwards compatible though and would process deletion
   jobs scheduled by the old code.

While testing for backwards compatibility is important, this commit removes
the job as it's not clear how to solve the problems. This unblocks further
fixes from being merged.

1 files changed, 0 insertions, 6 deletions

diff --git a/_support/get-previous-minor-release b/_support/get-previous-minor-release
deleted file mode 100755
index eaea20d7e..000000000
--- a/_support/get-previous-minor-release
+++ /dev/null
@@ -1,6 +0,0 @@
-#!/usr/bin/env ruby
-
-File.open("VERSION").read.scan(/(\d+)\.(\d+).\d+.*/) { |major_str, minor_str|
-  major, minor = major_str.to_i, minor_str.to_i
-  puts minor - 1 >= 0 ? "v#{major}.#{minor-1}.0" : "v#{major-1}.10.0"
-}