ref(metric-issues): Remove workflow-engine-metric-issue-ui flag usage

[malwilley]

Merge after #112422

This removes the flags completely from the backend

[github-actions]

Backend Test Failures

Failures on d04e64c in this run:

tests/sentry/workflow_engine/processors/test_workflow.py::TestProcessWorkflows::test_multiple_detectors__preferred — log

[gw1] linux -- Python 3.13.1 /home/runner/work/sentry/sentry/.venv/bin/python3
tests/sentry/workflow_engine/processors/test_workflow.py:460: in test_multiple_detectors__preferred
    assert result.data.triggered_workflows == {self.error_workflow}
E   assert {<Workflow at...929462759456>} == {<Workflow at...929462693922>}
E     
E     Extra items in the left set:
E     <Workflow at 0x7f2b92acf710: id=84, organization_id=4557929462759456>
E     
E     Full diff:
E       {
E     -     <Workflow at 0x7f2b89b76f90: id=83, organization_id=4557929462693922>,
E     ?                        - ^^^^
E     +     <Workflow at 0x7f2b92acd490: id=83, organization_id=4557929462693922>,
E     ?                         ^^^^^
E     +     <Workflow at 0x7f2b92acf710: id=84, organization_id=4557929462759456>,
E       }

tests/sentry/workflow_engine/processors/test_workflow.py::TestProcessWorkflows::test_no_detector — log

[gw1] linux -- Python 3.13.1 /home/runner/work/sentry/sentry/.venv/bin/python3
tests/sentry/workflow_engine/processors/test_workflow.py:332: in test_no_detector
    assert result.msg == "No Detectors associated with the issue were found"
E   AssertionError: assert 'No workflows... in the event' == 'No Detectors...ue were found'
E     
E     - No Detectors associated with the issue were found
E     + No workflows are associated with the detector in the event

tests/snuba/search/test_backend.py::EventsGenericSnubaSearchTest::test_no_feature — log

[gw1] linux -- Python 3.13.1 /home/runner/work/sentry/sentry/.venv/bin/python3
tests/snuba/search/test_backend.py:3512: in test_no_feature
    assert list(results) == []
E   assert [<Group at 0x...929468526624>] == []
E     
E     Left contains one more item: <Group at 0x7fb73f3ea210: id=243, project_id=4557929468526624>
E     
E     Full diff:
E     - []
E     + [
E     +     <Group at 0x7fb73f3ea210: id=243, project_id=4557929468526624>,
E     + ]