[Jobs] Remove assertion for one single controller resources.

[cblmemo]

A user reports when launch a managed jobs, following assertion error appears:

  File "sky/jobs/core.py", line 128, in launch
    assert len(controller_task.resources) == 1, controller_task
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

This is due to the multi-controller resources we introduces in #4053. Fixed now

Tested (run the relevant ones):

• Code formatting: bash format.sh
• Any manual or new tests for this PR (please specify below)
• All smoke tests: pytest tests/test_smoke.py
• Relevant individual smoke tests: pytest tests/test_smoke.py::test_fill_in_the_name
• Backward compatibility tests: conda deactivate; bash -i tests/backward_compatibility_tests.sh