Remove check_flit_worktree_compatibility once upstream flit fix ships

## Background PR #65771 adds `check_flit_worktree_compatibility` to `dev/breeze/src/airflow_breeze/prepare_providers/provider_distributions.py`. The check refuses to build provider sdists when the source tree is a git worktree, because two related things go wrong otherwise and no warning is emitted: 1. **flit worktree detection bug.** `flit.vcs.identify_vcs` only checks `.git.is_dir()`, missing the `.git`-as-file pointer that git uses for worktrees and submodules. flit silently falls back to a non-VCS sdist that omits tracked files (`docs/`, `tests/`, `provider.yaml`, anything declared in `[tool.flit.sdist] include`), and the resulting packages fail reproducibility checks against the released sdists on dist.apache.org. 2. **Breeze Docker-mount case.** Even once flit is fixed, when Breeze runs the build inside Docker only the worktree directory is bind-mounted — the absolute `gitdir:` path baked into the worktree's `.git` file references the main repo's `.git/worktrees/<name>` directory on the host, which is not reachable from the container. `git ls-files` then fails or misbehaves. Upstream flit tracking: - Issue: https://github.com/pypa/flit/issues/798 - PR: https://github.com/pypa/flit/pull/799 ## What to do when this issue is actioned Once **both** of the following hold: - [ ] The flit fix (pypa/flit#799) is merged and released. - [ ] Airflow's constraints pin to a flit release that contains the fix, **and** the Breeze Docker image is rebuilt to include that version. …and the Docker-mount case has been addressed (either by mounting the main repo's `.git/worktrees/<name>` directory alongside the worktree, or by rewriting the `gitdir:` pointer when sources are staged into the container, or by deciding the Docker-mount path is not supported from worktrees), remove: - `check_flit_worktree_compatibility` in `dev/breeze/src/airflow_breeze/prepare_providers/provider_distributions.py` - Its call site in `dev/breeze/src/airflow_breeze/commands/release_management_commands.p…