Releases: keep only latest and test pre-releases, no per-version releases #194

Development is continuous, and every v2/basic build already goes to the Telegram channel with its version and hash. The per-version releases v2.01…v2.10 (#157) are not needed.

Keep:

• latest: the newest v2 and basic builds plus decoder-v2-mapping.txt;
• pre-releases made by hand for testing with a reporter, such as flowufo-187-test1 (new feature: receiving udp video strem from cheap toys with wifi cam's #187). They are deleted when that test is over.

Change:

• CI: drop the Versioned release step. Upload to latest, Upload mapping (workflow artifact) and Telegram stay.
• Delete the releases v2.01…v2.10 and their tags.
• Docs (docs/testing.md, the three READMEs): no per-version releases. The change history is the merged pull requests and the commits of v2. Older binaries are in Telegram, and how to make a test pre-release is described.
• The version rule stays: 2.xx, +0.01 per app PR. The version shows in the menu, in /stats.json and in the Telegram post.