Remove all unprotected branches from Secure test projects

Problem to solve

The repos of the Secure test projects cumulate 600+ branches, including 380+ branches that don't seemed to be used for QA (they are neither -FREEZE nor master branch). Having that many branches makes it harder to focus on what needs to be maintained.

This is a one-shot cleanup. We might want to improve the docs, and remind developers they should remove the branches they create for testing purposes.

Proposal

• rename branches used for QA, and add the -FREEZE prefix; see
• remove all remote branches that are neither -FREEZE nor master

/cc @willmeek