Remove deprecated libfuzzer_coverage task (#2021)

- Remove the ability to create or execute a `libfuzzer_coverage` task
- Preserve the enum variant in `onefuzztypes` to prevent errors when deserializing old data
- Remove doc references to `libfuzzer_coverage`

src/pytypes/extra/generate-docs.py

@@ -236,7 +236,7 @@ def main() -> None:
                 ),
                 JobTaskStopped(
                     task_id=UUID(int=1),
-                    task_type=TaskType.libfuzzer_coverage,
+                    task_type=TaskType.coverage,
                 ),
             ],
         ),

src/pytypes/onefuzztypes/enums.py

@@ -151,7 +151,10 @@ class TaskState(Enum):
 class TaskType(Enum):
     coverage = "coverage"
     libfuzzer_fuzz = "libfuzzer_fuzz"
+
+    # Deprecated, kept for deserialization of old task data.
     libfuzzer_coverage = "libfuzzer_coverage"
+
     libfuzzer_crash_report = "libfuzzer_crash_report"
     libfuzzer_merge = "libfuzzer_merge"
     libfuzzer_regression = "libfuzzer_regression"