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.

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/overrides/IrExternalOverridabilityCondition.kt

@@ -10,7 +10,6 @@ import org.jetbrains.kotlin.ir.declarations.IrOverridableMember
 interface IrExternalOverridabilityCondition {
     enum class Result {
         OVERRIDABLE,
-        CONFLICT,
         INCOMPATIBLE,
         UNKNOWN
     }
@@ -26,8 +25,6 @@ interface IrExternalOverridabilityCondition {
      *
      *   - [Result.OVERRIDABLE] means that it is definitely overridable, and neither the general override checking algorithm, nor other
      *     external overridability conditions can refute that.
-     *   - [Result.CONFLICT] means that it is an error to have both declarations available in the same class, so the compiler should report
-     *     an error.
      *   - [Result.INCOMPATIBLE] means that it is not overridable, but it's OK to have both declarations available in the same class because
      *     they don't cause a conflict.
      *   - [Result.UNKNOWN] means that this overridability condition cannot claim anything about the overridability, and the final result
@@ -42,7 +39,7 @@ interface IrExternalOverridabilityCondition {
      * Specifies what values can be returned by [isOverridable]. Used as an optimization to reorder overridability conditions to prevent
      * redundant calculations.
      *
-     *   - [Contract.CONFLICTS_ONLY] means that [isOverridable] can return [Result.CONFLICT], [Result.INCOMPATIBLE] or [Result.UNKNOWN].
+     *   - [Contract.CONFLICTS_ONLY] means that [isOverridable] can return [Result.INCOMPATIBLE] or [Result.UNKNOWN].
      *   - [Contract.SUCCESS_ONLY] means that [isOverridable] can return [Result.OVERRIDABLE] or [Result.UNKNOWN].
      *   - [Contract.BOTH] means that [isOverridable] can return any result.
      */

compiler/ir/ir.tree/src/org/jetbrains/kotlin/ir/overrides/IrOverrideChecker.kt

@@ -158,7 +158,6 @@ class IrOverrideChecker(
                 externalCondition.isOverridable(superMember, subMember)
             when (result) {
                 OVERRIDABLE -> wasSuccess = true
-                CONFLICT -> return conflict("External condition failed")
                 INCOMPATIBLE -> return incompatible("External condition")
                 UNKNOWN -> {}
             }
@@ -173,7 +172,6 @@ class IrOverrideChecker(
             val result =
                 externalCondition.isOverridable(superMember, subMember)
             when (result) {
-                CONFLICT -> return conflict("External condition failed")
                 INCOMPATIBLE -> return incompatible("External condition")
                 OVERRIDABLE -> error(
                     "Contract violation in ${externalCondition.javaClass} condition. It's not supposed to end with success"

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: