Purge branches

[echavarria-lrz]

@kayaercument

1. testing has to become develop
2. All other branches should be deleted

[burgholzer]

Because it is kind of related: Is there any particular reason for not using main as the default branch throughout all of the repositories? Most services for CI, etc. kind of assume that main is the default branch name by now (up until a couple years the default was master) and require extra configuration for other default names. If there is no particular reason for choosing develop, I would argue that we should stick to the default here.

[ystade]

Resolved in the meantime.