FIR LC: identifier is not compiled element

FIR LC uses KtLightClassForDecompiledDeclaration instead,
when it is asked to convert compiled element to light element.
Such decompiled declaration delegates things to Class stub, where
ClsIdentifierImpl, a subtype of PsiCompiledElement, will be used.

analysis/symbol-light-classes/src/org/jetbrains/kotlin/light/classes/symbol/FirLightIdentifier.kt

@@ -6,7 +6,6 @@
 package org.jetbrains.kotlin.light.classes.symbol
 
 import com.intellij.openapi.util.TextRange
-import com.intellij.psi.PsiCompiledElement
 import com.intellij.psi.PsiElement
 import com.intellij.psi.PsiFile
 import com.intellij.psi.impl.light.LightIdentifier
@@ -25,7 +24,7 @@ internal class FirLightIdentifier(
 ) : LightIdentifier(
     lightOwner.manager,
     (firSymbol as? KtNamedSymbol)?.name?.identifierOrNullIfSpecial
-), PsiCompiledElement, PsiElementWithOrigin<PsiElement> {
+), PsiElementWithOrigin<PsiElement> {
 
     override val origin: PsiElement?
         get() = when (val ktDeclaration = firSymbol?.psi) {
@@ -38,7 +37,6 @@ internal class FirLightIdentifier(
             else -> null
         }
 
-    override fun getMirror(): PsiElement? = null
     override fun isPhysical(): Boolean = true
     override fun getParent(): PsiElement = lightOwner
     override fun getContainingFile(): PsiFile = lightOwner.containingFile