FIR: get rid of effectively unused AccessorSymbol

compiler/fir/tree/src/org/jetbrains/kotlin/fir/symbols/SyntheticSymbol.kt

@@ -5,11 +5,5 @@
 
 package org.jetbrains.kotlin.fir.symbols
 
-import org.jetbrains.kotlin.name.CallableId
-
 interface SyntheticSymbol
 
-interface AccessorSymbol {
-    val callableId: CallableId // it's an id of related property (synthetic or not)
-    val accessorId: CallableId // it's an id of accessor function
-}

compiler/fir/tree/src/org/jetbrains/kotlin/fir/symbols/impl/FirFunctionSymbol.kt

@@ -11,8 +11,6 @@ import org.jetbrains.kotlin.fir.declarations.*
 import org.jetbrains.kotlin.fir.expressions.FirDelegatedConstructorCall
 import org.jetbrains.kotlin.fir.references.FirControlFlowGraphReference
 import org.jetbrains.kotlin.fir.references.FirResolvedNamedReference
-import org.jetbrains.kotlin.fir.symbols.AccessorSymbol
-import org.jetbrains.kotlin.fir.symbols.FirBasedSymbol
 import org.jetbrains.kotlin.fir.symbols.ensureResolved
 import org.jetbrains.kotlin.name.CallableId
 import org.jetbrains.kotlin.name.FqName
@@ -84,8 +82,8 @@ class FirConstructorSymbol(
 
 open class FirAccessorSymbol(
     callableId: CallableId,
-    override val accessorId: CallableId
-) : FirPropertySymbol(callableId), AccessorSymbol
+    open val accessorId: CallableId
+) : FirPropertySymbol(callableId)
 
 // ------------------------ unnamed ------------------------
 
@@ -99,6 +97,4 @@ class FirAnonymousFunctionSymbol : FirFunctionWithoutNameSymbol<FirAnonymousFunc
 
 class FirPropertyAccessorSymbol : FirFunctionWithoutNameSymbol<FirPropertyAccessor>(Name.identifier("accessor"))
 
-class FirPropertyFieldDeclarationSymbol() : FirBasedSymbol<FirBackingField>()
-
 class FirErrorFunctionSymbol : FirFunctionWithoutNameSymbol<FirErrorFunction>(Name.identifier("error"))