IR, descriptors: remove (Ir)ExternalOverridabilityCondition.Result.CONFLICT

No existing external overridability condition reports a conflict anyway,
and there's no support for it in the IR case.

core/descriptors/src/org/jetbrains/kotlin/resolve/ExternalOverridabilityCondition.java

@@ -23,7 +23,7 @@ import org.jetbrains.kotlin.descriptors.ClassDescriptor;
 
 public interface ExternalOverridabilityCondition {
     enum Result {
-        OVERRIDABLE, CONFLICT, INCOMPATIBLE, UNKNOWN
+        OVERRIDABLE, INCOMPATIBLE, UNKNOWN
     }
 
     enum Contract {

core/descriptors/src/org/jetbrains/kotlin/resolve/OverridingUtil.java

@@ -258,8 +258,6 @@ public class OverridingUtil {
                 case OVERRIDABLE:
                     wasSuccess = true;
                     break;
-                case CONFLICT:
-                    return OverrideCompatibilityInfo.conflict("External condition failed");
                 case INCOMPATIBLE:
                     return OverrideCompatibilityInfo.incompatible("External condition");
                 case UNKNOWN:
@@ -280,8 +278,6 @@ public class OverridingUtil {
             ExternalOverridabilityCondition.Result result =
                     externalCondition.isOverridable(superDescriptor, subDescriptor, subClassDescriptor);
             switch (result) {
-                case CONFLICT:
-                    return OverrideCompatibilityInfo.conflict("External condition failed");
                 case INCOMPATIBLE:
                     return OverrideCompatibilityInfo.incompatible("External condition");
                 case OVERRIDABLE: