Eliminate some warnings (mostly redundant is checks in whens)

compiler/frontend/src/org/jetbrains/kotlin/psi/codeFragmentUtil.kt

@@ -38,8 +38,7 @@ fun KtElement.suppressDiagnosticsInDebugMode(): Boolean {
 var KtFile.suppressDiagnosticsInDebugMode: Boolean
     get() = when (this) {
         is KtCodeFragment -> true
-        is KtFile -> getUserData(SUPPRESS_DIAGNOSTICS_IN_DEBUG_MODE) ?: false
-        else -> false
+        else -> getUserData(SUPPRESS_DIAGNOSTICS_IN_DEBUG_MODE) ?: false
     }
     set(skip) {
         putUserData(SUPPRESS_DIAGNOSTICS_IN_DEBUG_MODE, skip)

compiler/ir/backend.common/src/org/jetbrains/kotlin/backend/common/lower/DefaultArgumentStubGenerator.kt

@@ -350,7 +350,7 @@ private fun FunctionDescriptor.generateDefaultsFunction(context: CommonBackendCo
                         /* annotations           = */ annotations,
                         /* isPrimary             = */ false,
                         /* source                = */ source)
-            is FunctionDescriptor -> {
+            else -> {
                 val name = Name.identifier("$name\$default")
 
                 SimpleFunctionDescriptorImpl.create(
@@ -360,7 +360,6 @@ private fun FunctionDescriptor.generateDefaultsFunction(context: CommonBackendCo
                         /* kind                  = */ CallableMemberDescriptor.Kind.SYNTHESIZED,
                         /* source                = */ source)
             }
-            else -> TODO("FIXME: $this")
         }
 
         val syntheticParameters = MutableList(valueParameters.size / 32 + 1) { i ->