Bug 1634484 - [ci] Remove the 'bugbug_all_low' shadow-scheduler and related strategy, r=marco

Differential Revision: https://phabricator.services.mozilla.com/D73328

taskcluster/ci/source-test/shadow-scheduler.yml

@@ -44,17 +44,6 @@ bugbug_all:
         env:
             TASKGRAPH_OPTIMIZE_STRATEGIES: taskgraph.optimize:experimental.bugbug_all
 
-bugbug_all_low:
-    description: Runs the bugbug_all optimization strategy (with a low confidence threshold) instead of the default.
-    treeherder:
-        symbol: SS(bugbug_all_low)
-    index:
-        product: source
-        job-name: shadow-scheduler-bugbug_all_low
-    worker:
-        env:
-            TASKGRAPH_OPTIMIZE_STRATEGIES: taskgraph.optimize:experimental.bugbug_all_low
-
 bugbug_all_high:
     description: Runs the bugbug_all optimization strategy (with a high confidence threshold) instead of the default.
     treeherder:

taskcluster/taskgraph/optimize/__init__.py

@@ -401,11 +401,6 @@ class experimental(object):
     }
     """Doesn't limit platforms, medium confidence threshold."""
 
-    bugbug_all_low = {
-        'test': Any('skip-unless-schedules', 'bugbug-low', split_args=tuple),
-    }
-    """Doesn't limit platforms, low confidence threshold."""
-
     bugbug_all_high = {
         'test': Any('skip-unless-schedules', 'bugbug-high', split_args=tuple),
     }