Fixes editing of non-indicator rules

If the user edits a rule without visiting the About tab, they will
receive a value of threatIndicatorPath: '' which we'll then try to send
to the backend, but it gets rejected.

By removing this defaulting logic we get the correct behavior: existing
rules default to threatIndicatorPath: undefined, which gets stripped
before being sent to the backend. If the rule is an indicator rule, the
value will be persisted as expected.

x-pack/plugins/security_solution/public/detections/components/rules/step_about_rule/default_value.ts

@@ -29,7 +29,6 @@ export const stepAboutDefaultValue: AboutStepRule = {
   license: '',
   ruleNameOverride: '',
   tags: [],
-  threatIndicatorPath: '',
   timestampOverride: '',
   threat: threatDefault,
   note: '',

x-pack/plugins/security_solution/public/detections/pages/detection_engine/rules/helpers.test.tsx

@@ -116,7 +116,6 @@ describe('rule helpers', () => {
         severity: { value: 'low', mapping: fillEmptySeverityMappings([]), isMappingChecked: false },
         tags: ['tag1', 'tag2'],
         threat: getThreatMock(),
-        threatIndicatorPath: '',
         timestampOverride: 'event.ingested',
       };
       const scheduleRuleStepData = { from: '0s', interval: '5m' };

x-pack/plugins/security_solution/public/detections/pages/detection_engine/rules/helpers.tsx

@@ -180,7 +180,7 @@ export const getAboutStepsData = (rule: Rule, detailsView: boolean): AboutStepRu
     },
     falsePositives,
     threat: threat as Threats,
-    threatIndicatorPath: threatIndicatorPath ?? '',
+    threatIndicatorPath,
   };
 };