docs(quickstart): remove deprecated tmux version notice

why: Support for tmux < 3.2 has been dropped.
what:
- Remove deprecation notice for tmux 1.8 - 3.1
- Keep 3.2a as minimum requirement

Author: tony

docs/quickstart.md

@@ -12,8 +12,7 @@ from inside a live tmux session.
 
 ## Requirements
 
-- [tmux] 3.2a or newer (recommended)
-  - tmux 1.8 - 3.1 are deprecated and will be unsupported in a future release
+- [tmux] 3.2a or newer
 - [pip] - for this handbook's examples
 
 [tmux]: https://tmux.github.io/