Remove subgraph callable

[fjetter]

With dask/dask#11568 the SubgraphCallable is now effectively dead code. There is just one exception since the optimization optimization.fuse.subgraphs is on by default for the legacy dataframe.

Sibling in dask/dask dask/dask#11575

[fjetter]

• revert 26a9239

[github-actions]

Unit Test Results

See test report for an extended history of previous test failures. This is useful for diagnosing flaky tests.

     7 files   -     22       7 suites   - 22   1h 39m 33s ⏱️ - 10h 38m 37s
 3 922 tests  -    208   3 742 ✅  -    272  179 💤 +   68  1 ❌  - 4 
10 955 runs   - 44 884  10 094 ✅  - 43 312  860 💤  - 1 566  1 ❌  - 6 

For more details on these failures, see this check.

Results for commit 26a9239. ± Comparison against base commit 5e0ea69.

This pull request removes 208 tests.

distributed.cli.tests.test_dask_scheduler ‑ test_dashboard
distributed.cli.tests.test_dask_scheduler ‑ test_dashboard_allowlist
distributed.cli.tests.test_dask_scheduler ‑ test_dashboard_non_standard_ports
distributed.cli.tests.test_dask_scheduler ‑ test_dashboard_port_zero
distributed.cli.tests.test_dask_scheduler ‑ test_defaults
distributed.cli.tests.test_dask_scheduler ‑ test_hostport
distributed.cli.tests.test_dask_scheduler ‑ test_idle_timeout
distributed.cli.tests.test_dask_scheduler ‑ test_interface
distributed.cli.tests.test_dask_scheduler ‑ test_multiple_protocols
distributed.cli.tests.test_dask_scheduler ‑ test_multiple_workers
…

This pull request skips 80 tests.

distributed.cli.tests.test_dask_worker ‑ test_dashboard_non_standard_ports
distributed.deploy.tests.test_local ‑ test_bokeh[False]
distributed.deploy.tests.test_local ‑ test_bokeh[True]
distributed.deploy.tests.test_local ‑ test_bokeh_kwargs
distributed.deploy.tests.test_local ‑ test_duplicate_clients
distributed.deploy.tests.test_local ‑ test_ipywidgets
distributed.deploy.tests.test_local ‑ test_ipywidgets_loop
distributed.deploy.tests.test_subprocess ‑ test_raise_on_windows
distributed.diagnostics.tests.test_eventstream ‑ test_eventstream
distributed.diagnostics.tests.test_task_stream ‑ test_get_task_stream_plot
…