infra: deprecation plan for packagecloud

[Totktonada]

https://packagecloud.io/tarantool now provides the following repositories:
1_6, 1_7, 1_9, 1_10, 2x (it is 2.1 in fact), 2_2, 2_3, 2_4.

Our S3 based infrastructure provides: 1.10, 2.1, 2.2, 2.3, 2.4, 2.5.

download.tarantool.org redirects 1.10-2.5 to S3 based repos and other repos to
packagecloud.io (it is 1.6, 1.7 and 1.9 so).

We should not create new repos on packagecloud (for 2.5+) and so it
worth to remove deployment to 2.5 from current master.

The question is what to do with 1.6-2.4 packagecloud repositories.

My proposal:

• Remove 2.5 deployment from master branch in tarantool.
• Prepare deployment script for Travis-CI, place it to the modulekit repository (luakit / ckit both) (I started to do it within this task).
• Move 1_6, 1_7, 1_9 to S3 based repos.
• Update all modules, connectors and other packages (say, small) that rely on packagecloud repo (enable it or push to it).
• Remove deployment to packagecloud on all branches (1.10-2.4).
• Drop packagecloud repositories at all to catch remaining problems.

Are there any objections?

Since pushing to packagecloud is performed from Travis-CI jobs, the issue #4894 is related here.

Follows up #3380.